Current fetcher has annoying "SRCREVINACTION" deadlock,
which occurs when SRCREV=${AUTOREV}=@bb.fetch.get_srcrev():
get_srcrev()->setup_localpath()->srcrev_internal_helper()
->evaluate SRCREV->get_srcrev()
current fetcher resolve the deadlock by introducing a
"SRCREVINACTION" condition check. Althoguh it works, it is
indeed not clean.
This patch use antoehr idea to break the deadlock: break
the dependency among SRCREV and get_srcrev(), i.e. assign
a specific keyword "AUTOINC" to AUTOREV. when Fetcher meet
this keyword, it will check and set the latest revision to
urldata.revision. get_srcrev later can use the urldata.revision
for value evaluation(SRCPV etc). In this case, SRCREV no longer
depends on get_srcrev, and there is not deadlock anymore.
