prs: use the PRServer to replace the BB_URI_LOCALCOUNT functionality

- adapt the PRServer to generate an incremental number for every revision set
associated with a (PN, PV)
- use one incrementing value rather than several
- PV becomes 0.1+gitAUTOINC+deadbeefdecafbad_decafbaddeadbeef
- if PV contains 'AUTOINC' set PKGV to the same thing with AUTOINC replaced
with the "auto PR" value
- if the PRServer isn't running replace AUTOINC with 0 (no package feeds, but usual
image creation would work)
- use the PR table with "AUTOINC-${PV-without-SRCREVs}" as key
- modify prexport/primport to address the generated srcrev entries
- this patch addresses the following proposal:
http://lists.linuxtogo.org/pipermail/bitbake-devel/2012-November/003878.html



Signed-off-by: Constantin Musca <constantinx.musca@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>