gitignore + posix.mak

1)
added to gitignore web and 2.*.ddoc as they're autogenerated
2)
the build didn't seem to work on OSX at least (from a fresh start using ./tools/update.sh method) because of 
git fetch --tags git@github.com:D-Programming-Language/dmd && \
which didn't work:
Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
posix.mak:27: *** Could not fetch latest version.  Stop.

so I modified posix.mak to instead get a GIT_HOME from the caller ( ./tools/update.sh)
I'm also making a pull request that gives that GIT_HOME (in tools.git/update.sh)

3)
gsoc13 references are undefined and prevent building; I'm removing them for now