Fix biggest memory leaks in NS-port. More remain.

Fix biggest memory leaks in NS-port.  More remain.

* emacs.c (ns_pool): New variable.
(main): Assign ns_pool.
(Fkill_emacs): Call ns_release_autorelease_pool.

* nsfns.m (x_set_background_color): Assign return value from
ns_index_color to face-background instead of NSColor*.
(ns_implicitly_set_icon_type): Fix indentation.
Change assignment in for loop to comparison.

* nsfont.m (ns_spec_to_descriptor): Fix indentation,
autorelease fdesc, release fdAttrs and tdict.
(ns_get_covering_families): Release charset.
(ns_findfonts): Release NSFontDescriptor created with new.
(ns_uni_to_glyphs): Fix indentation.
(setString): Release attrStr before assigning new value.

* nsmenu.m (ns_update_menubar): Call free_menubar_widget_value_tree
before returning.

* nsterm.m (x_free_frame_resources): Release
f->output_data.ns->miniimage
(ns_index_color): Fix indentation.  Do not retain
color_table->colors[i].