Add an assertion to guard against invalid use of svn_subst_detect_eol().
Add an assertion to guard against invalid use of svn_subst_detect_eol().

* subversion/libsvn_subr/subst.c
  (svn_subst_detect_eol): We should consider converting this function to
   take a pointer and a buffer size argument, instead of two pointers which
   define the buffer's boundaries. For now, just add an assert which if
   triggered indicates a bug in the caller.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion