[Windows only]
for System.Directory / Compat.Directory functionality that probes the OS
for local details re: misc user directories, perform late binding of
SHGetFolderPath() from shell32.dll, as it may not be present.
(cf. ghc-6.4's failure to operate on Win9x / NT boxes.) If the API isn't
there, fail with UnsupportedOperation.
Packages.readPackageConfigs: gracefully handle excns from getAppUserDataDirectory.

Merge to STABLE.