That place is git-revision.c; git-revision.c now lives in lib/log.
Also fix the compilation rules so that all object files that need
micro-revision.i depend on it.
This is a very gentle commit that just lays the groundwork in the
build system: it puts the include files to build libtor-app.a into
src/core, and to build the tor executable into src/app. The
executable is now "src/app/tor".
