Bug fix to r3240 which added contig_insert_bases() function to perform
multi-base insertions. This was used by shuffle pads and join editor
align button.

MAJOR ERROR: It produced alignment errors downstream where the next
bin started as that was still ch->pos++ instead of ch->pos += nbases.

Also tidied up the logic surrounding reference base coordinates,
although less of a major issue. I'm still not 100% certain refpos
updates are correct though.


git-svn-id: https://staden.svn.sourceforge.net/svnroot/staden/staden/trunk@3271 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1