Separate test function for mobile browsers?

[slightlyoff]

suchi.isOld currently detects only desktop browsers, with the regexes expressly handling only desktop OSes. We need to decide:

1. If we want a different test function for mobile laggards, and if so what it should be called (and should suchi.isOld() be renamed as a result?
2. What sort of language might be appropriate in a mobile prompt, since your options are likely to be much more limited and/or hard to use. E.g., installing a new browser on iOS often means being stuck on the old engine, so the only upgrade path that's reasonable is an OS upgrade. For Android, installing a new browser and choosing to use it for all browsing may not be straightforward (even by desktop standards).