source tree. Allows CRYPTOBASE to be set in mk.conf or environment.
If it's not set, it searches for: crypto-us, crypto-intl in that order.
Setting CRYPTOBASE to none forces a no-crypto build. EXPORTABLE_SYSTEM
is supported for backwards-compatibility.
Will be used in a forthcoming mega-commit which significantly improves
the build process when building a crypto-enabled system, and allows
for the international crypto sub-tree to be seamlessly integrated into
the build process.
thorpej