Add .gitignore everywhere based on .cvsignore.

* .gitignore: New.
* build-aux/.gitignore: New.
* data/.gitignore: New.
* doc/.gitignore: New.
* etc/.gitignore: New.
* examples/.gitignore: New.
* examples/calc++/.gitignore: New.
* lib/.gitignore: New.
* m4/.gitignore: New.
* po/.gitignore: New.
* runtime-po/.gitignore: New.
* src/.gitignore: New.
* tests/.gitignore: New.

m4/.gitignore

@@ -0,0 +1,63 @@
+/absolute-header.m4
+/argmatch.m4
+/config-h.m4
+/dirname.m4
+/dos.m4
+/double-slash-root.m4
+/error.m4
+/exitfail.m4
+/extensions.m4
+/getopt.m4
+/gettext.m4
+/gnulib-cache.m4
+/gnulib-common.m4
+/gnulib-comp.m4
+/gnulib-tool.m4
+/hash.m4
+/iconv.m4
+/include_next.m4
+/inline.m4
+/intlmacosx.m4
+/inttypes-h.m4
+/inttypes-pri.m4
+/inttypes.m4
+/javacomp.m4
+/javaexec.m4
+/lib-ld.m4
+/lib-link.m4
+/lib-prefix.m4
+/localcharset.m4
+/longlong.m4
+/malloc.m4
+/mbrtowc.m4
+/mbstate_t.m4
+/mbswidth.m4
+/nls.m4
+/po.m4
+/progtest.m4
+/quote.m4
+/quotearg.m4
+/stdbool.m4
+/stdint.m4
+/stdint_h.m4
+/stdio-safer.m4
+/stdlib_h.m4
+/stpcpy.m4
+/strerror.m4
+/string_h.m4
+/strndup.m4
+/strnlen.m4
+/strtol.m4
+/strtoul.m4
+/strverscmp.m4
+/unistd-safer.m4
+/unistd_h.m4
+/unlocked-io.m4
+/warning.m4
+/wchar.m4
+/wchar_t.m4
+/wctype.m4
+/wcwidth.m4
+/wint_t.m4
+/xalloc.m4
+/xstrndup.m4