Makefile.inc1:

• New file. Adds logic to search for the git binary, as well as determining the branch and revision, used in various places.

Makefile:

• Remove searching for the svn{,lite} binary.

Makefile.ec2:

• Reduce duplicated code, removing searching for the svn{,lite} binary, in addition to EC2_SVN{BRANCH,REV}.
• Rename EC2_SVN* with GIT* for consistency.

Makefile.mirrors:

• Remove the SRCBRANCH declaration, replaced with the exported GITBRANCH variable.
• Update _SNAP_SUFFIX from SVNREVISION to GITREV, and remove the leading 'r' from it, since it will break git hashes.
• Remove yet another instance of duplicated code to search for the svn{,version}lite binary.

Sponsored by: Rubicon Communications, LLC (netgate.com)