Fix a few problems with common naming:
* Move toolset requirements code from toolsets plus common-variant-tag into a separate toolset::requirements. This fixes inconsistency problems with libraries that have names that don't match the real content.
* Remove custom stlport code in msvc-strport toolset and use common stlport.jam. This normalizes the settings and requirements for stlport builds.
Also added support for removing the version related info, tolset and version tag, to support --layout=system install option.
[SVN r24427]
Rene Rivera