Detect Go version and abort if less than 1.3

Our Go code is making use of Go 1.3 features (e.g. sync.Pool). Check
what version of the Go compiler was found, and if not at least 1.3
print an error (and abort the build):

    -- Found dtrace in /usr/sbin/dtrace
    -- Found Go compiler: /usr/local/bin/go (1.3.3)
    CMake Error at tlm/cmake/Modules/FindCouchbaseGo.cmake:27 (MESSAGE):
    Go version of 1.3 or higher required (found version 1.2.2)

Change-Id: Id7e1ce67dc06cd4db072b33a469e5d855eeae32e
Reviewed-on: http://review.couchbase.org/44226
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>