fixed vertical scrollbar in message widget for the case of a single message that is bigger than the height of the widget

adding the function RunTests to each python unittest allows that the
test is executed either with the default TestRunner or an XMLTestRunner
for producing an XML output file. With no command line argument, the
default Runner is used (same behaviour as previously), with 'xml' as
the first argument, the XMLTestRunner is used.

- show legend if specified
- allow setting of y_range when plotting only 1D data
- allow setting of x and y axis labels when plotting only 1D data
- allow setting an empty string as title

- 3D plots are generated also if no plot_if is specified
- use matplotlib natural neighbour interpolation instead of linear,
  since latter works only on regularly spaced (in both dimensions)
  output grids

- fix assign column type as string (not str) if pattern doesn't match
- allow more complicated headers (with special characters)
- add some test cases

the maximum number of labels to display can now be set using
the optional argument 'max_num_labels'

write out charmm style pdb format if chain name or residue name is too
long for standard pdb format

1. The plotting function takes a **kwargs to pass custom
   parameters to pyplot.plot()
2. plot_if can be set to a callable to filter the rows of the
   table before plotting.

1. We now read traditional CSV files. Since the files do not explicitly
   specify the column format, we have to guess the format of each column
   after importing.
2. For efficient serialization, table data can be pickled/unpickled
   directly.

changed baseline value for test image in img io tests to expose more rounding errors on old machines

Queries like 'rname=GLY and aname=CA' get faster by 5x.
Sometimes it's a good idea to review old code...