Update the bidirectional reordering engine for Unicode 6.3 and 7.0.

Update the bidirectional reordering engine for Unicode 6.3 and 7.0.

 src/bidi.c (bidi_ignore_explicit_marks_for_paragraph_level): Remove
 variable.
 (bidi_get_type): Return the isolate initiators and terminator
 types.
 (bidi_isolate_fmt_char, bidi_paired_bracket_type)
 (bidi_fetch_char_skip_isolates, find_first_strong_char)
 (bidi_find_bracket_pairs, bidi_resolve_brackets): New functions.
 (bidi_set_sos_type): Renamed from bidi_set_sor_type and updated
 for the new features.
 (bidi_push_embedding_level, bidi_pop_embedding_level): Update to
 push and pop correctly for isolates.
 (bidi_remember_char): Modified to accept an additional argument
 and record the bidi type according to its value.
 (bidi_cache_iterator_state): Accept an additional argument to only
 update an existing state.  Handle the new members of struct bidi_it.
 (bidi_cache_find): Arguments changed: no lnger accepts a level,
 instead accepts a flag telling it whether it is okay to return
 unresolved neutrals.
 (bidi_initialize): Initiate and staticpro the bracket-type uniprop
 table.  Initialize new isolate-related members.
 (bidi_paragraph_init): Some code factored out into
 find_first_strong_char.
 (bidi_resolve_explicit_1): Function deleted, its code incorporated
 into bidi_resolve_explicit.
 (bidi_resolve_explicit): Support the isolate initiators and
 terminator.  Fix handling of embeddings and overrides according to
 new UBA requirements.  Record information about previously seen
 characters here (moved from bidi_level_of_next_char).
 (bidi_resolve_weak): Adapt to changes in struct members.
 (FLAG_EMBEDDING_INSIDE, FLAG_OPPOSITE_INSIDE, MAX_BPA_STACK)
 (STORE_BRACKET_CHARPOS, PUSH_BPA_STACK): New macros.
 (bidi_resolve_neutral): Call bidi_resolve_brackets to handle the
 paired bracket resolution.  Handle isolate initiators and
 terminator.
 (bidi_type_of_next_char): Remove unneeded code for BN limit.
 (bidi_level_of_next_char): Move the code that records information
 about previous characters to bidi_resolve_explicit.  Fix logic of
 resolving neutrals and make sure their cache entries are updated.
 Remove now unneeded special handling of PDF level.
 src/dispextern.h (struct glyph): Enlarge the width of resolved_level.
 (BIDI_MAXDEPTH): New macro, renamed from BIDI_MAXLEVEL and
 enlarged per Unicode 6.3.
 (enum bidi_bracket_type_t): New data type.
 (struct bidi_saved_info): Leave only 2 type members out of 4.
 Remove bytepos.
 (struct bidi_stack): Add members necessary to support isolating
 sequences.
 (struct bidi_it): Add new members necessary to support isolating
 sequences and bracket pair resolution.
 src/xdisp.c (Fbidi_resolved_levels): New function.
 (syms_of_xdisp): Defsubr it.
 (append_glyph, append_composite_glyph, produce_image_glyph)
 (append_stretch_glyph, append_glyphless_glyph): Convert aborts to
 assertions.
 (syms_of_xdisp) <inhibit-bidi-mirroring>: New variable.
 src/term.c (append_glyph, append_composite_glyph)
 (append_glyphless_glyph): Convert aborts to assertions.
 src/.gdbinit (pgx): Display the character codepoint, resolved level,
 and bidi type also for glyphless glyphs.

 lisp/simple.el (what-cursor-position): Update to support the new bidi
 characters.
 lisp/descr-text.el (describe-char): Update to support the new bidi
 characters.

 admin/unidata/unidata-gen.el (unidata-prop-alist): New properties
 'paired-bracket' and 'bracket-type', in support of the UBA 6.3.
 (unidata-gen-table): Support PROP-IDX being a function.
 (unidata-describe-bidi-bracket-type, unidata-gen-brackets-list)
 (unidata-gen-bracket-type-list): New functions.
 (unidata-check): Support checking the 'bracket-type' attribute.
 (unidata-gen-files): Don't create backups for uni-*.el files.
 admin/unidata/Makefile.in (${unidir}/charprop.el): Depend on
 BidiMirroring.txt and BidiBrackets.txt.
 admin/unidata/BidiBrackets.txt: New file, from Unicode.

 etc/NEWS: Mention the UBA implementation update.
 etc/HELLO: Remove now unneeded directional control characters.

 doc/lispref/nonascii.texi (Character Properties): Document the new
 properties 'bracket-type' and 'paired-bracket'.
 doc/lisprefdisplay.texi (Bidirectional Display): Update the version of the
 UBA to which we are conforming.

 test/BidiCharacterTest.txt: New file, from Unicode.
 test/biditest.el: New file.