build system: support automatic reconfiguration for autotools user

This series aims at improving the user experience for those people who (like me) use that Autotools-based interface to the build system of Git.

The two actual improvements (equipped with proper explanations and rationales) are implemented in the last two patches. The other five patches are just preparatory changes.

The series as general or as clean as it could actually be, but it's enough to scratch the itch that motivated me to write it.

Thanks,
Stefano

Stefano Lattarini (7):
autoconf: GIT_CONF_APPEND_LINE: change signature
autoconf: GIT_CONF_APPEND_LINE -> GIT_CONF_SUBST
autoconf: remove some redundant shell indirections
autoconf: remove few redundant semicolons
autoconf: use AC_CONFIG_COMMANDS instead of ad-hoc 'config.mak.append'
build: "make clean" should not remove configure-generated files
build: reconfigure automatically if configure.ac changes

 Makefile     | 17 +++++++++++++++--
 configure.ac | 53 ++++++++++++++++++++++++++++++-----------------------
 2 files changed, 45 insertions(+), 25 deletions(-)

1.7.10.2.1067.g553d16e