respect limits when truncating URLs

Closes #248

Also modify pod for render_related_url to match 40-character limit in code [closes #249]
Merge pull request #251 from QUTlib/20140725-truncate_urls

respect limits when truncating URLs
Merge branch 'master' of https://github.com/eprints/eprints into 20140725-undef-in-render_related_url

Conflicts:
	perl_lib/EPrints/Extras.pm