This is to not need static variables, which could trip up users
with destruction order problems.

This potentially makes these operations slightly slower, but I
think they're infrequent enough that this should not be noticable.

Also there is one breaking API change, for a method that is not
used by any code in FlatBuffers and is assumed to affect very
few if any users. A namechange and comment ensures that those
affected, if any, will not run into trouble silently.

Change-Id: I16c1352d1dfc9092c816ddb7e353ed7f5f417444
Tested: on Linux.