maint: add git hook scripts

We find it worthwhile to use consistent commit summary prefixes.
To that end, the commit-msg script requires that all commits I make
start with "$P: " (where $P is one of ~100 programs in coreutils)
or one of a few other words, like gnulib tests maint doc build.
It allows more than one word, so e.g., "cat tail head: " would also
be accepted.  Pádraig Brady wrote the initial version, with its
72-column and blank-if-present second line checks.
The pre-commit script is the same as the git-supplied sample script,
modulo a bug fix and the "exec 1>&2" redirection.
* scripts/git-hooks/commit-msg: New file.
* scripts/git-hooks/pre-commit: New file.
* scripts/git-hooks/applypatch-msg: New file.  Verbatim from .sample.
* cfg.mk: Exempt two of the new scripts from the no-leading-TABs check,
since they're nearly verbatim from git, and we want to stay in sync.
Exempt the commit-msg script from the no-"fail=0" check.

1 files changed, 6 insertions, 4 deletions

diff --git a/cfg.mk b/cfg.mk
index c3102be71..fa7f84488 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -384,13 +384,15 @@ exclude_file_name_regexp--sc_file_system = \
 exclude_file_name_regexp--sc_prohibit_always_true_header_tests = \
   ^m4/stat-prog\.m4$$
 exclude_file_name_regexp--sc_prohibit_fail_0 = \
-  (^tests/init\.sh|Makefile\.am|\.mk)$$
+  (^scripts/git-hooks/commit-msg|^tests/init\.sh|Makefile\.am|\.mk)$$
 exclude_file_name_regexp--sc_prohibit_atoi_atof = ^lib/euidaccess-stat\.c$$
+
+tbi_1 = ^tests/pr/|(^gl/lib/reg.*\.c\.diff|Makefile(\.am)?|\.mk|^man/help2man)$$
+tbi_2 = ^scripts/git-hooks/(pre-commit|applypatch-msg)$$
 exclude_file_name_regexp--sc_prohibit_tab_based_indentation = \
-  ^tests/pr/|(^gl/lib/reg.*\.c\.diff|Makefile(\.am)?|\.mk|^man/help2man)$$
+  $(tbi_1)|$(tbi_2)
+
 exclude_file_name_regexp--sc_preprocessor_indentation = \
   ^(gl/lib/rand-isaac\.[ch]|gl/tests/test-rand-isaac\.c)$$
-
-
 exclude_file_name_regexp--sc_prohibit_stat_st_blocks = \
   ^(src/system\.h|tests/du/2g)$$