Added an ArrayPush macro. Basically it's just a short-hand for
appending to the end of an array.


git-svn-id: svn://svn.code.sf.net/p/staden/code/staden@3581 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1
Optimised contig_insert_base2 and contig_delete_base2.  The main
change is avoiding recomputing contig ends all the while. Often we can
work out what the change will be (eg we're in a bin in the middle of
the contig) and it's only at the boundary bins where it gets more
complex. So we avoid brute force calculations where possible.

Also updated contig_shift_base to accept +N and -N to shift by more
than 1 bp.


git-svn-id: svn://svn.code.sf.net/p/staden/code/staden@3582 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1