Rewrite UndoToString to use glib funcs
GFileReadAll → g_file_get_contents
Dup UTF-8 variant of GIOCreate
Add file name conversion warning in GIOCreate8
Link to gnulib and add appropriate header, due to usage of xzalloc
Rewrite GFD_NewDir to use glib string funcs
Unify char view & bitmap view menu IDs
Partially combine Metrics View menu ID with existing one
Move Menu IDs away from charview_private.h

All menu IDs are now moved to fontforge/menu.h, and using enum for less
management overhead. Remaining func declarations are moving to
fontforgeexe/ folder.
Merging of remaining menu IDs from other widgets
Move looks_like_uri() to gutils, will be useful in more places
Rewrite FontViewSetTitle() to use glib
Solidify GXDrawSetWindowTitles8()

Adds error checking, use glib string funcs
Use Xutf8SetWMProperties() if available
Cosmetic cond check & debug mesg in GXDrawGetWindowTitle8()
putenv/setenv → g_setenv

Also replaced a few getenv → g_getenv. Don't check unused funcs in
configure.ac
Let go of the cryptic "-psn_" option
getFontForgeUserDir → g_get_user_config_dir

The other possible getFontForgeUserDir() params have never been used
anyway, and glib has covered those cases if needed in future.
GFileGetHomeDocumentsDir → g_get_user_special_dir
Drop crude debug mesg during startup, do proper debug later
Drop orphaned gRGB2HSL()