specl: update ordinalSuffix () error specs to match the new error messages.

* specs/string_ext_spec.lua (describe string.ordinalSuffix): Make the
expectations match reality.
string_ext: bail out early with fatal type mismatch errors.

* src/string_ext.lua (wrap): Rather than letting the guts of wrap
choke unpredictably later on, assert the required types at the
outset.
(tfind): Likewise.  These currently bubble up to finds and split
as well.
specl: ensure that failing to meet specs kills make distcheck.

* specs/lib/specl.lua (run): Return true unless there are
expectation failures.
* specs/specl: Exit with non-zero status for with expectation
failures.
specs: add missing specs for string.finds and string.tfind.

* specs/string_ext_spec.lua (describe string.finds (), describe
string.tfind ()): New specs for these APIs.