Do not remove anchors in safe_mode

[tetafro]

This PR fixes the following:

>>> markdown('[text](#anchor)')
u'<p><a href="#anchor">text</a></p>\n'

>>> markdown('[text](#anchor)', safe_mode='escape')
u'<p><a href="#">text</a></p>\n'

In other words - internal anchors should not be considered unsafe.

Also I've added pygments tag to fenced_code_blocks_leading_lang_space test because it fails without pygments installed.

[nicholasserra]

Looks good to me, thanks!