generator: Implement BufferIn parameter type (RHBZ#501889). The BufferIn argument turns into various things: in C const char *, size_t parameter pair in XDR an opaque<> type (instead of string) which allows \0 chars in other bindings mostly just a string, since most languages except for C permit strings to contain any 8 bit data
New API calls: truncate, truncate_size, mkdir_mode, utimens, lchown. truncate, truncate_size: Used to truncate files to a particular size, or to zero bytes. mkdir_mode: Like mkdir but allows you to also specify the initial permissions for the new directory. utimens: Set timestamp on a file with nanosecond accuracy. lchown: Corresponding to lchown(2) syscall (we already have chown). The implementation is complicated by the fact that we had to add an Int64 parameter type to the generator.
Add tests for bindings parameters, fix several broken bindings.