(mount_slash): Eliminated.
(mount_info::read_mounts): Eliminate looking up existing entries. The
loop for deleting cygpath entries is done only when such entries exist.
(mount_info::from_registry): Eliminate sorting.
(mount_info::add_item): Call add_reg_mount if necessary. Check nmounts
more precisely. Use strcasematch in looking up existing entries.
(mount_info::del_item): Call del_reg_mount if necessary. Use
strcasematch. Use memmove instead of memcpy.
(mount_info::import_v1_registry): Everything is done in this method.
(mount_info::to_registry): Eliminated.
(mount_info::from_v1_registry): Eliminated.
(cygwin_umount): Simply call del_item.
shared.h: Modify the declaration of add_item and del_item. Remove the
declaration of from_v1_registry.
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