apply the FileSystemEncoding when passing filename to FFI code

This fixes a crash when running addWatch on a FilePath that contains
characters not valid in the current encoding. For example, 'ü' is not
valid in the C locale.
adjust base dependency for FileSystemEncoding

Base 4.5.0.0 was shipped with GHC 7.4.1, which should be
the first version to support this.
Bump to version 0.3.6