set search input to readonly when disable_search_threshold is met
Revert 6dc024dc5db3f449da30a1b13dade665e33278dc - which stupidly
assumed that Prototype and jQuery could do anything the same way. How
did this get merged in the first place? UGH.
Merge pull request #1294 from koenpunt/gh1293-disable-search-input

Read-only search field when search is disabled.
Merge branch 'master' into fix-proto-scrollcalc-bug

Conflicts:
	public/chosen.proto.min.js
Merge pull request #1301 from harvesthq/fix-proto-scrollcalc-bug

Fix scroll bug in Prototype version
Merge branch 'master' into fix-rtl-positioning