- Experimental correction of zigzag-like small drifts, don't sure it is better, than current drift correction

git-svn-id: svn://svn.code.sf.net/p/gwyddion/code/trunk/gwyddion@16798 25697fe4-d644-49b8-9d30-be5465f2adf3
- Actually add zigzag.c

git-svn-id: svn://svn.code.sf.net/p/gwyddion/code/trunk/gwyddion@16799 25697fe4-d644-49b8-9d30-be5465f2adf3
- Removed incomplete code from previous commits

git-svn-id: svn://svn.code.sf.net/p/gwyddion/code/trunk/gwyddion@16800 25697fe4-d644-49b8-9d30-be5465f2adf3