bug fixed:

a bug prevented the correct plotting of several files each containing multiple blocks of data.
An identical name of the tmp files used to dump each block of data was used when handling each of the
data files (output.1, output.2) so that new data blocks overwrote the old one, causing the disappeareance
of the latter: in practice only on data file was plotted.

Fixed by adding a random integer number to naming convention.
handle function of single columns as an argument of the -u option
see help message for more details.

It is now possible to apply on the fly some function defined in XMGRACE
to a single column by specifying that in the -u option, e.g.
plot -u1:'cos($2)' file.dat

This is achieved by analyzing the argument of -u option: if that is not a number
the corresponding operation is added to the batch file and used to plot the
n-th data block.

This is still EXPERIMENTAL and should not be used for multiple data sets or files.
Merge branch 'integrate_trans'

Conflicts:
	xplot
version 2.0

This version fixes a number of bug in the previous version 1.0.
- better handling of multi-sets (block of data) files.
- simpler coding of the batch file construction.
- handle column function of a single argument in the option -u (see help)
- safe use of temporary files.