Introduce the svn_cstring_join2() API that allows selecting if the trailing separator is required in the joined string.
Previously, svn_cstring_join() has been always appending the trailing separator, and that required us to sometimes manually strip that final separator from the result.
* subversion/include/svn_string.h (svn_cstring_join2): New, revved from ... (svn_cstring_join): ...this function, which is now deprecated.
* subversion/libsvn_subr/string.c (svn_cstring_join2): New, supports the new 'trailing_separator' argument. (svn_cstring_join): Move ...
* subversion/libsvn_subr/deprecated.c (svn_cstring_join): ...here and call svn_cstring_join2() with the 'trailing_separator' set to true, to match the original behavior.
* subversion/tests/libsvn_subr/string-test.c (test_cstring_join): New test. (test_funcs): Add new test.
* subversion/libsvn_repos/hooks.c (svn_repos__hooks_start_commit): Use svn_cstring_join2() without the trailing separator, instead of manually stripping it from the resulting string. (svn_repos__hooks_post_lock, svn_repos__hooks_post_unlock): Switch to svn_cstring_join2(), request the trailing separator as before.
* tools/dev/svnmover/svnmover.c (execute): Switch to svn_cstring_join2(), request the trailing separator as before.