Merge branch 'jn/make'

Merge branch 'jn/make'

* jn/make:
  Set datarootdir in config.mak.in
  Quote all calls to GIT_CONF_APPEND_LINE
  Typofix in configure.ac comment.
  configure.ac vertical whitespace usage cleanup
  autoconf: Checks for some programs
  autoconf: Checks for libraries
  autoconf: Checks for some library functions.
  autoconf: Checks for typedefs, structures, and compiler characteristics.
  autoconf: Preparing the way for autodetection
  Copy description of build configuration variables to configure.ac
  Teach make clean about configure and autoconf
  autoconf: Use autoconf to write installation directories to config.mak.autogen