Now building IECoreRI regardless of compiler version (at IE).

We need to build IECoreRI so we can read/write PTCs in Houdini 13 (which uses a different compiler). Since I removed the compiler version guard, but didn't modify the install paths (we decided not to for now), its possible to build the procedural and display driver with a different compiler, overwriting the versions we actually want. Currently we are just throwing those away (by installing to /tmp when the compiler doesn't match). If we want them in the future, we need to change the install paths.
Initializing defaultObjectPoolCache later in plugin load.

It seems that HoudiniDSOInit is called several times during startup, one of which seems to be in a forked process or something, and we end up with 2 versions of the UT_Cache registered. This results in a broken Cache Manager UI. By moving the cache init to a different function, it only gets called once, and all works as expected.
Added a sanity check to IECore::DeepImageConverter.
Fixed an off-by-one bug.
Merge pull request #230 from andrewkaufman/cacheManager

Initializing defaultObjectPoolCache later in plugin load.
Merge pull request #229 from andrewkaufman/dlMultiCompiler

Building IECoreRI regardless of compiler version (at IE).
Merge pull request #231 from goddardl/DeepImageFix

Simple DeepImageConverter fixes.