Three fixes for hashtable seeding on Windows

First, wrap "advapi32.dll" into the TEXT() macro. If UNICODE is defined,
GetModuleHandle() redirects to GetModuleHandleW(), which excepts a wchar_t*
UTF-16 parameter, thus causing a compile error. TEXT() prefixes the string
literal with L in this case, and does nothing otherwise.

Second, make sure that CryptGenRandom() is actually called through the function
pointer retrieved by the call to GetProcAddress() above.

And third, replace _getpid() with the equivalent and more ubiquitous Win32 API
function GetCurrentProcessId(). Since _getpid() is not exported by all C
runtimes on Windows (most notably the Driver Development Kit), using it might
introduce previously unneeded runtime dependencies. GetCurrentProcessId(), on
the other hand, has been available in kernel32.dll since at least Windows 95,
just like the other API functions used in this code (GetModuleHandle() and
GetProcAddress()).
Merge pull request #162 from nmlgc/master

Three fixes for hashtable seeding on Windows