Import wiredtiger-wiredtiger-2.8-rc2-253-g379ffab.tar.gz from wiredtiger branch mongodb-2.8
SERVER-16529 Coarser OperationContext scope for background threads

Cuts the number of instantions of operation contexts and increases the
chance that a given maintenance operation would be seen in db.currentOp.

This is just a cosmetic change.
SERVER-16428 Partition the WT session cache
SERVER-15357 Revert "Revert "SERVER-15357 Require GCC 4.8.2 now that our Solaris toolchain is updated""

This reverts commit b5d97eeeea4ef66731eb273bc484884452991acf.
Merge remote-tracking branch 'upstream/master'