Add debug code to the membuffer cache that detects disabled mutexes while there are concurrent write accesses.
Add debug code to the membuffer cache that detects disabled mutexes
while there are concurrent write accesses.

I ran into that situation when toying a round with multi-threaded
svnadmin operation.  It took me a while to figure out that svnadmin
created with cache in single-threaded mode, which caused random
crashes.

* subversion/libsvn_subr/cache-membuffer.c
  (svn_membuffer_t): Add a write lock counter.
  (svn_cache__membuffer_cache_create): Initilize the counter.
  (membuffer_cache_set_internal): Use assertions to update and check
                                  the new counter.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1795322 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion