(check_path_access): Use passed in path_conv buf.
(get_full_path_of_dll): Use passed in name buf to avoid a static. Rip out most
of the path checking since LoadLibrary will do all of this automatically.
(dlopen): Set errno when appropriate (may not be compliant?).
* environ.cc (posify): Don't pass in "native" path if it seems to actually be
posix.