SERVER-13429 Use logging system in mongod signal handlers, test exit logging.

Still not really safe for signal handlers, but no worse than before,
and correctly logs to the log file/syslog, so an improvement.

(cherry picked from commit f4e6aa9ee7c0dccbb4789d3dff1d92b086d67b88)
SERVER-13429 Eliminate rawOut and related functions

(cherry picked from commit 4e1eccfe64f424daead6ed22542377d2e1ce798e)
SERVER-13429 Remove printStackAndExit

All of the functions in signal_handlers.cpp were broken when logfiles or
syslog were in use. This commit removes them and all callers. The files were
left in place for a later commit to fill them back in with a unified signal
handling system.

(cherry picked from commit 11e43325fa2b0139df1eb9c367b984a5b112dbb4)
SERVER-13429 unify signal handling between mongos and mongod

(cherry picked from commit ad91eb0f75f39c1bb71b5e0ca4279b883cb9fe8d)
SERVER-13429 Update exit_logging.js to also test mongos exit logging.

(cherry picked from commit 9e041ccf433660008ed2ddb1c2ed58ba78ef5488)
SERVER-13448 broadcast updates/deletes to all shards when more than one targeted
(cherry picked from commit 9b17edd15ffb0ba3a3a9309fafd9bd4fa04a4d92)
SERVER-12550: use Context instead of ReadContext and don't check shard version
              this happens later
SERVER-12242 SERVER-12244 Fix typo in compact/reIndex error messages

The error messages originally were incorrectly swapped with one
another.

(cherry picked from commit df0236cab083063fd125e289c6bac6b017bc6b67)
Revert "SERVER-13383 validateKeyPattern allow only numeric/string key types"

This reverts commit b48e15efdd02c3217356484ad462dcde9d57920d.
BUMP 2.6.0-rc3
Merge remote-tracking branch 'upstream/v2.6' into v2.6