add support for redirecting private library routines via hooks

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on October 23, 2013 14:46:51_

Today all our private library redirection is via import replacement.
However, there are cases where a lib calls its own routines directly and we
want to replace them. E.g., in issue #450 we need to replace priv kernel32's
GetModuleFileName. For issue #1292 , intercepting LdrLoadDll was sufficient, but
there is a bunch of extra work in kernelbase calling its own LoadLibraryExW
such that we may want a hook interceptor there.

These redirection hooks need not have any of the sophistication of
general-purpose monitoring hooks: these are just replacements. If we don't
need to call the original function (which I think we should move away from,
even though some redirection today calls the original to handle corner
cases) we can just put in a jmp and never remove it.

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1298_