* cygheap.cc (cygheap_root::cygheap_rot): Remove constructor.

* cygheap.cc (cygheap_root::cygheap_rot): Remove constructor.
(cygheap_root::~cygheap_root): Remove destructor.
(cygheap_root::operator =): Remove.
(cygheap_root::set): New method.
* cygheap.h (cygheap_root): Reflect above changes.  Store root info in
mount-like structure.
(cygheap_root:posix_ok): New method.
(cygheap_root::ischroot_native): Ditto.
(cygheap_root::unchroot): Ditto.
(cygheap_root::exists): Ditto.
(cygheap_root::posix_length): Ditto.
(cygheap_root::posix_path): Ditto.
(cygheap_root::native_length): Ditto.
(cygheap_root::native_path): Ditto.
* dir.cc (opendir): Remove special chroot test.
* path.cc (path_prefix_p): Remove front end.
(normalize_posix_path): Reorganize chroot tests to accomodate new convention of
allowing paths using posix chroot prefix.
(path_conv::check): Pass a "already ran normalize" option to
conv_to_win32_path.  Return if there is an error from this function.
(mount_info::conv_to_win32_path): Add extra argument.  Don't call
normalize_posix_path if caller has already done so.  Substitute chroot setting,
if any, for root translation.  Add chroot checking to final output step.
* shared_info (mount_info): Accomodate additional argument to
conv_to_win32_path.
* syscalls.cc (chroot): Store both normalized posix path and native path in
chroot.