StrCoreAlloc* and StrAlloc*Secure

Rename the StrAllocate* functions to StrCoreAlloc* to make it easier to tell them apart from the original StrAlloc* methods.

Add the StrAlloc*Secure methods back as wrappers around the StrCoreAlloc* functions.
Is this other approach better? https://github.com/rseanhall/wix3/commit/0ed5bdc4d95e109ed2fd437f2148d277dd352cdb