For things like 'gmake davautocheck' use the specified make program
for the nested make.

* Makefile.in
  (davautocheck, svnserveautocheck): Set MAKE environment variable.

* subversion/tests/cmdline/davautocheck.sh: Use MAKE environment
   variable if set.

* subversion/tests/cmdline/svnserveautocheck.sh: Use MAKE environment
   variable if set.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1576848 13f79535-47bb-0310-9956-ffa450edef68