Add support for Intel 15, fix Glob Bug, and compiler path selection bug.

This patch fixes 3 issues:

* Adds support for Intel-15 so MSVC version can be auto-selected.
* Changes GLOB to path.glob as for some reason the GLOB rule always fails when used in this context (discovered when testing this patch).
* Changes selection logic for target-types variable - previous code used the value of PROCESSOR_ARCHITECTURE to detect this, but that appears to only tell you which sub-system bjam is running in.  For example on my system bjam is a 32-bit app (default for an msvc build), but I only have the Intel 64-bit compiler installed (under /intel64/).  New logic checks whether the intel64 compiler exists and uses that if it is - Intel's installer won't install this on 32 bit platforms in which case the glob fails and things fall back to the ia32-intel64 cross compiler when address-model=64 is specified.