Webform does not check that block module is enable

Hi all,

Found a bug while making a new site. This site has no block module enabled.

2 issues (and maybe other side effect) :

• "Available as block" still displayed in form settings
• When submitting settings form, it end up with an error, saying block_load does not exists in webform.pages.inc, function webform_configure_form_submit_save, line 520. This function does not check if block module is enable before doing.

Hope it'll help make Webform better, and thank you for this marvellous work !