[FIXED JENKINS-18268] Pass alternativeUrl during validation and renamed alternativeUrl help file.
Merge pull request #25 from tyrius02/master

[FIXED JENKINS-18268] Pass alternativeUrl during validation and renamed the alternativeUrl help file.
Rename alternative URL help file to match field name (and thus actually show up on the settings page)

Update help description for link URL
Add alternative URL validation to config validation method.
Add URL validation to constructor
Merge branch 'master' of https://github.com/jenkinsci/jira-plugin

Conflicts:
	src/main/resources/hudson/plugins/jira/JiraSite/help-alternativeUrl.html