update 3-forms.md

adds the missing "/" in the url
BUG Fix edge case IE8 / dev / ssl / download file crash
Prevents issue at http://support.microsoft.com/kb/323308 appearing on dev
Merge pull request #3069 from tractorcow/pulls/3.1-ie8-download-ssl-crash

BUG Fix edge case IE8 / dev / ssl / download file crash
Merge pull request #3067 from sanjaymundhra/patch-7

update 3-forms.md
API Make default gridfield paging configurable
Documentation improved
Merge pull request #3026 from tractorcow/pulls/3.1-gridfield-paging

API Make default gridfield paging configurable