Fix topo devices with same short_name

Display devices in the topology map with the same short_name as
distinct nodes.

Fixes redmine #1822
Add as_canon Graphviz format

This is useful for debugging graph building
Update graph edge directions for device topo

Adjust the graph edges so that "Up" devices appear to the left and
"Down" devices appear to the right.

Fixes redmine #1824
Add 'minlen' option for topo graphs

Running build_topo_graph.pl with -m 2 increases the spacing between the
nodes and makes it less likely for the interface names to overlap.

Fixes redmine #1821 if you update your topo crontab entries to add -n -m 2
Add line length setting in device topo view

Makes it easier to see interface names if "Show Interface Names?" has
been selected
Options for rebuilding whole topo graphs

Add options 'Show Interface Names' and 'Line Length' when rebuilding the
whole topo graphs in the GUI

Fixes redmine #1821
Uncomment LoadModule for apache 2.2

Reverts part of 3408e2a and fixes redmine #1817
Merge pull request #19 from candlerb/candlerb/1817

Uncomment LoadModule for apache 2.2
Merge pull request #17 from candlerb/candlerb/1822

Topo fixes #1822 #1824
Fixes for #1818
Swap head/tail on "up" links

Previous change for #1824 ended up with head/tail labels on the wrong ends
Merge pull request #20 from candlerb/candlerb/1821

Improvements to topology graphs
Merge pull request #21 from candlerb/candlerb/1822bis

Swap head/tail on "up" links