Merge branch 'jc/install-no-hardlinks'

Your build platform may support hardlinks but you may prefer not to use
them, e.g. when installing to DESTDIR to make a tarball and untarring on
a filesystem that has poor support for hardlinks.

The Makefile in git-gui project may need to learn to honor the same
setting; it unconditionally creates git-citool by hardlinking git-gui.

* jc/install-no-hardlinks:
  Makefile: NO_INSTALL_HARDLINKS

diff --cc Makefile
Simple merge