Fixes to 2field preconditioning

Solver now ensures that the variable and time-derivatives
have the same boundary condition.

2field example was broken by last change to preconditioning
Fix to petsc laplace solver
Adding .gitattributes and modify .gitignore

Try to prevent future line-ending changes showing up in repo

Adding .CVS and .svn to .gitignore
Adding floor(Field, value) function

Works on Field2D and Field3D
IDL routines for reading and writing strings to NetCDF

Previously would write as CHAR, rather than char array. Now
defines a length, writes the string, then converts when reading.