graph_format with multiple formats
Currently the option graph_format only allows only one format at a time to be selected. This can be a strong limitation (assume one wants both eps for latex and fig to handle and edit plots).
We should allow multiple entries with a preprocessor syntax
The preprocessor would define the variable in options_ as:
options_.graph_format = char('eps', 'fig' );
which would properly be handled in dyn_saveas by changing strcmp with strmatch.