Add PS Vita port.

Thanks to Anton Stenmark.
Merge branch 'master' into v2.1
FFI: Another fix for cdata equality comparisons.
Merge branch 'master' into v2.1
x64: Workaround for MSVC build issue.
Merge branch 'master' into v2.1
Fix frame traversal while searching for error function.
Merge branch 'master' into v2.1
Fix FOLD rule for STRREF of SNEW.
FFI: Fix recording of indexing a struct pointer ctype object itself.
Merge branch 'master' into v2.1
Fix FOLD rule for string.sub(s, ...) == k.
Merge branch 'master' into v2.1
Merge remote-tracking branch 'luajit/v2.1' into stable+box+feeder
Fix typo
Fix SEGV: service_find_code(, -1) should not return stub record with cb == NULL
Fix counter overflow & wording: processed_rows may overflow on long running replicas, leading to wrong "loading/0%" status
Compat: restore previous semantic of ctuple() and decode_varint32