* fhandler.h (fhandler_cygdrive:DRVSZ): New enum.

* fhandler.h (fhandler_cygdrive:DRVSZ): New enum.
(pdrive_buf): New place to hold information about cygdrive.
* fhandler_disk_file.cc (fhandler_cygdrive::set_drives): Store drive info in
pdrive_buf since get_win32_name() could now be too small to hold everything.
(fhandler_cygdrive::rewinddir): Reset pdrive to pdrive_buf.
(fhandler_cygdrive::closedir): Ditto.
* pipe.cc (fhandler_pipe::init): Be more defensive when referencing
get_win32_name().  Rework logic which made a copy of the POSIX path and then
never used it.