Correct regexp matching of raw bytes

Correct regexp matching of raw bytes

Make regexp matching of raw bytes work in all combination of unibyte
and multibyte patterns and targets, as exact strings and in character
alternatives (bug#3687).

* src/regex-emacs.c (analyze_first):
Include raw byte in fastmap when pattern is a multibyte exact string.
Include leading byte in fastmap for raw bytes in character alternatives.
(re_match_2_internal):
Decrement the byte count by the number of bytes in the pattern character,
not 1.
* test/src/regex-emacs-tests.el (regexp-unibyte-unibyte)
(regexp-multibyte-unibyte, regexp-unibyte-mutibyte)
(regexp-multibyte-multibyte): New tests.