Adapting Makefile to assure appcache build

It's important that the version number in appcached and index/mobile files are the same. By making appcache build depend on index/mobile, this is assured.

@oterral I stumbled upon this during some tests. You might rebuild index.html, but not appcache...and your appcache is dead.
Hmm. Then how did I arrive in a state where the version in the appcache file (path version) did not correspond to the version in the index.html file?