Merge branch 'ab/build-gitweb'

Merge branch 'ab/build-gitweb'

Teach "make all" to build gitweb as well.

* ab/build-gitweb:
  gitweb/Makefile: add a "NO_GITWEB" parameter
  Makefile: build 'gitweb' in the default target
  gitweb/Makefile: include in top-level Makefile
  gitweb: remove "test" and "test-installed" targets
  gitweb/Makefile: prepare to merge into top-level Makefile
  gitweb/Makefile: clear up and de-duplicate the gitweb.{css,js} vars
  gitweb/Makefile: add a $(GITWEB_ALL) variable
  gitweb/Makefile: define all .PHONY prerequisites inline