Allow to disable all svn_cache__t in maintainer mode via an envvar.  I need
this sometimes when debugging segfaults inside FSFS.

Currently, cache writes are not affected; only cache reads are intercepted.

* notes/knobs
  (SVN_X_DOES_NOT_MARK_THE_SPOT): New envvar.

* subversion/libsvn_subr/cache.c
  (svn_cache__get, svn_cache__get_partial, svn_cache__iter):
    If SVN_DEBUG and SVN_X_DOES_NOT_MARK_THE_SPOT, pretend the cache is empty.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1461689 13f79535-47bb-0310-9956-ffa450edef68
* subversion/libsvn_subr/cmdline.c
  (svn_cmdline_init): Hook a few more error types to stderr in debug mode.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1461690 13f79535-47bb-0310-9956-ffa450edef68