Merge branch 'sl/autoconf'

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