Make GimpRecaptcha check be case-insensitive

Users report new captcha case-sensitivity as counter-intuitive.
The fix is to simply ignore case when doing the comparison.

Fix bug #11377.
Add missing CHANGELOG entry for #10724 to 0.1.1.
Merge remote-tracking branch 'wfn/bug11377_gimpcaptcha' into develop
Add CHANGELOG entry for #11377.
Whitespace fixes in CHANGELOG.