Introduce -M to set the FSFS cache size for file:// URLs with
svnsync.  The cache could already be controlled via the config
file, and the command line config support, so '-M' is a short
form of '--config-option config:miscellany:memory-cache-size='.

* subversion/svnsync/svnsync.c
  (svnsync_cmd_table): Add 'M' to synchronize and copy-revprops.
  (svnsync_options): Add 'M'.
  (sub_main): Handle '-M' and update the config.

* tools/client-side/bash_completion
  (_svnsync): Add -M.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1579922 13f79535-47bb-0310-9956-ffa450edef68