libmount: add function for context userdata

Signed-off-by: Karel Zak <kzak@redhat.com>
pylibmount: cleanup cxt usage

Signed-off-by: Karel Zak <kzak@redhat.com>
pylibmount: remove Context_get_table()

It's too problematic and too low-level to support it Py binding.

Signed-off-by: Karel Zak <kzak@redhat.com>
libmount: add reference counting to libmount_fs

 * mnt_new_fs() returns object with refcount=1
 * mnt_free_fs() does not care about reference counter

 * new functions mnt_ref_fs() and mnt_unref_fs()

 * mnt_table_add_fs() and mnt_table_rem_fs() uses reference counter

 * libmmnt_context uses reference counter for internal FS (as it could be
   shared outside the context)

 * backwardly incompatible change:

	- FS could be deallocated after mnt_table_remove_fs()

 * it's recommended to use mnt_unref_fs() after mnt_table_add_fs()

Signed-off-by: Karel Zak <kzak@redhat.com>
fsck: use libmount fs reference counter

Signed-off-by: Karel Zak <kzak@redhat.com>
libmount: add reference counting to libmnt_cache

Signed-off-by: Karel Zak <kzak@redhat.com>
misc: use libmnt_cache reference counting

Signed-off-by: Karel Zak <kzak@redhat.com>
libmount: add reference counter to libmnt_table

Signed-off-by: Karel Zak <kzak@redhat.com>
misc: use libmnt_table reference counter

Signed-off-by: Karel Zak <kzak@redhat.com>