build: Turn update-po.sh into a Makefile rule

Suggested by Andreas Stricker in:
<https://lists.gnu.org/archive/html/bug-gettext/2014-04/msg00020.html>.
* configure.ac (maintainer-update-po): New recursive rule.
* update-po.sh: Remove.
* autogen.sh: Don't mention update-po.sh.
* Makefile.am (maintainer-update-po-local): New rule.
* gettext-runtime/Makefile.am (maintainer-update-po): New rule.
* gettext-runtime/man/Makefile.am (update-man1): Remove; add explicit
dependency on the executable to each .1 rule.
* gettext-tools/man/Makefile.am (update-man1): Remove; add explicit
dependency on the executable to each .1 rule.
examples: Don't use KDE build infrastructure when generating POT
tests: Add work around for newer Bison version used in autopoint test

* autopoint-3 (gettext_datadir): Don't regenerate intl/plural.c.
tests: Don't run a test only successful after "make dist" by default

* Makefile.am (TESTS): Move xgettext-1 to...
(EXTRA_DIST): ...here.
format-python-brace: Limit acceptable format specifiers
scheme: Recognize GIMP script-fu extension _"abc"

* gettext-tools/src/x-scheme.c (read_object): Recognize _"abc".
intl: Define PRI_MACROS_BROKEN if undefined

* loadmsgcat.c (PRI_MACROS_BROKEN) [_LIBC]: Define to 0, if
undefined.
maint: Remove duplicate files from the repository
Makefile.in.in: Make dependencies of a PO file and 'dist' customizable

* Makevars (POFILESDEPS): New variable.
(DISTFILESDEPS): New variable.
* Makefile.in.in ($(POFILES)): Depend on $(POFILESDEPS) instead of
$(srcdir)/$(DOMAIN).pot.
(dist distdir): Run $(DISTFILEDEPS) instead of 'update-po'.
Makefile.in.in: Add an option to claim the package as GNU/non-GNU
Reporeted by David Shea at:
<https://savannah.gnu.org/bugs/?40520>.
* Makevars (PACKAGE_GNU): New variable.
* Makefile.in.in ($(DOMAIN).pot-update): Don't search for "GNU
packagename" if $(PACKAGE_GNU) is set.
Update ChangeLog.
Makefile.in.in: Turn {POFILES,DISTFILES}DEPS into yes/no options

Preserve the previous behavior even if a user forgot to update
Makevars, after calling autopoint.
* Makevars (PO_DEPENDS_ON_POT): Rename from POFILESDEPS and turn
it into a yes/no option.
(DIST_DEPENDS_ON_POT): Rename from DISTFILESDEPS and turn it into
a yes/no option.
maint: Update Admin/plans
Makefile.in.in: Rename DIST_DEPENDS_ON_POT to DIST_DEPENDS_ON_UPDATE_PO
Fix commit 4dc36d2f
xgettext: Factor out commonly used mixed_string_buffer

* x-python.c (init_mixed_string_buffer)
(mixed_string_buffer_append_byte)
(mixed_string_buffer_append_unicode_grow)
(mixed_string_buffer_append_unicode)
(mixed_string_buffer_flush_utf16_surr)
(mixed_string_buffer_flush_curr_buffer)
(mixed_string_buffer_append, mixed_string_buffer_result)
(free_mixed_string_buffer): Move to...
* xgettext.c: ...here.
(mixed_string_buffer_alloc): Rename from init_mixed_string_buffer.
(mixed_string_buffer_append_to_curr_buffer): Rename from
mixed_string_buffer_append_byte.
(mixed_string_buffer_append_to_utf8_buffer): Rename from
mixed_string_buffer_append_unicode.
(mixed_string_buffer_grow_utf8_buffer): Rename from
mixed_string_buffer_append_unicode_grow.
(mixed_string_buffer_append_char): Split from
mixed_string_buffer_append.
(mixed_string_buffer_append_unicode): Split from
mixed_string_buffer_append.
(mixed_string_buffer_done): New function merging
mixed_string_buffer_result and free_mixed_string_buffer.
* xgettext.h (mixed_string_buffer): New struct moved from
x-python.c; add logical_file_name and line_number fields.
(mixed_string_buffer_alloc): New function declaration.
(mixed_string_buffer_append_char): New function declaration.
(mixed_string_buffer_append_unicode): New function declaration.
(mixed_string_buffer_done): New function declaration.
* x-javascript.c (init_mixed_string_buffer)
(mixed_string_buffer_append_byte)
(mixed_string_buffer_append_unicode_grow)
(mixed_string_buffer_append_unicode)
(mixed_string_buffer_flush_utf16_surr)
(mixed_string_buffer_flush_curr_buffer)
(mixed_string_buffer_append, mixed_string_buffer_result)
(free_mixed_string_buffer): Remove.
vala: Support C99-style Unicode escapes
xgettext: Add more comments to mixed_string_buffer usage
xgettext: Fix memleaks around wrong usage of mixed_string_buffer_done