Merge branch 'jn/makefile-cleanup'

Tightens dependency rules to avoid unnecessary recompilation, and cleans up our Makefile in general. * jn/makefile-cleanup: Makefile: document ground rules for target-specific dependencies Makefile: move GIT-VERSION-FILE dependencies closer to use Makefile: build instaweb similar to other scripts Makefile: update scripts when build-time parameters change Makefile: do not replace @@GIT_VERSION@@ in shell scripts Makefile: split prefix flags from GIT-CFLAGS Makefile: be silent when only GIT_USER_AGENT changes Makefile: split GIT_USER_AGENT from GIT-CFLAGS Makefile: do not replace @@GIT_USER_AGENT@@ in scripts Makefile: apply dependencies consistently to sparse/asm targets Makefile: do not have git.o depend on common-cmds.h Makefile: fold XDIFF_H and VCSSVN_H into LIB_H Makefile: fold MISC_H into LIB_H Makefile: sort LIB_H list