Fix compiler warning in repos library C tests.

Technically, I could just cast the calculation of max_logs to an (int).  But
this seems more correct to me.  An unlimited log run could return more logs than
a signed int can hold.  We can't possibly return more logs than svn_revnum_t can
hold.  For the purposes of a test it doesn't matter.  However, I view our tests
as also example code and if someone was following this example in a real
implementation I think this code would lead them down a path with potential
problems.  The potential infinite loop issue doesn't apply to real examples
becuase nobody loops the possible limit values except in tests.

* subversion/tests/libsvn_repos/repos-test.c
  (get_logs): Update max_logs, num_logs and num_expected to be svn_revnum_t.
  (log_receiver): Update the type of the baton to match get_logs().



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1570038 13f79535-47bb-0310-9956-ffa450edef68