matchers: recognize non-table inequality sooner in objcmp.

Replace lost section from objcmp reordering in b234584:
* lib/specl/matchers.lua (objcmp): Recognize inequality of non-
table objects sooner.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
specs: be more tolerant to differeng Lua error message formats.

* specs/specl_spec.yaml: Some versions report `'=' expected` and
others `syntax error` for the example code in the spec; use
`match_error` rather than `contain_error` to accept either.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>