Enable incremental builder to find files that moved, and try to process them via patch + rename, instead of delete + add.

b/11437930

Change-Id: I984349fbc9a8dac4379e00c0d66fc7d22c4eb834
Verify a ZIP's MD5 with the value from an existing ".md5sum" file.

Most ROMs ship a ".md5sum" file instead of ".md5". Adding ".md5sum" as
fallback option thus makes it easier for people to safely install ZIPs
as they don't have to rename a file.
Merge branch 'twrp2.7-support-md5sum-file' into twrp2.7