Standardize indentation of multiline 'if'/'elseif' conditions

Always indent the continuation one level deeper, and always place the
closing parenthesis on the next line, per coding conventions.
https://www.mediawiki.org/wiki/Manual:Coding_conventions#Indenting_and_alignment
https://www.mediawiki.org/wiki/Manual:Coding_conventions#Line_continuation

Regexp used: (\t+)(if|while|\} elseif|foreach).+(?<![;}])\n\1\S

Also:
* Change to just one line if line length stays under 100 characters.
* Add "// Do nothing" comment in empty 'if' bodies.
* Change '#' comments to '//' comments near affected code.

Change-Id: I4f62658fddb5a0ed18bbf9b2231cd794683d6402