Allow compound (AND) conditions in mc.ext to disambiguate overloaded extensions

[zaytsev]

It would be awesome if someone did something to ts - right now it is always regarded as a video file. This might have been reasonable before the advent of TypeScript?, but now most of TS-files are actually code.

shell/i/.ts
type/^data$
    Open=...

zaytsev@parallels:~/src/app/src$ file main.ts 
main.ts: Java source, ASCII text

zaytsev@parallels:~/src/app/src$ file typings.d.ts 
typings.d.ts: ASCII text

zaytsev@parallels:~/src/app/src$ file test.ts 
test.ts: Java source, UTF-8 Unicode text

zaytsev@parallels:~/src$ file sample_640x360.ts 
sample_640x360.ts: data

zaytsev@parallels:~/src$ file ed24p_10.ts 
ed24p_10.ts: data

file qt/translations/qt_ru.ts
qt/translations/qt_ru.ts: XML 1.0 document, UTF-8 Unicode text, with very long lines

Spun off from #4128.