fio2gnplot: Print specific message if cmdline parsing fails

If the cmdline isn't consistent regarding the getopt, let's print a
specific message to inform user about this situation instead of printing
the help.

Showing the help without any specific message was very confusing.
fio2gnuplot: Adding getoplong support for cmdline

Help message was misleading since long options were not supported....
This patch adds all the long options to be supported.
fio2gnuplot: Fixing typo in error message
fio2gnuplot: Adding verbose option

Reducing default's verbosity and add a -v option to increase it.
This avoids flooding end-users and let an option for thoses who need to
get a complete trace.
fio2gnuplot: Deleting temporary files by default
fio2gnuplot: Managing temporary files in a better way

If gnuplot success at rendering, let's delete all temporary files.
If gnuplot fails at rendering, let's keep all temporary files.
If user don't want to run gnuplot, let's keep temporary files.
If user ask to keep the temporary files (option -k), let's always keep
them.
fio2gnuplot: Fixing help message

Adding missing features & fix indent
fio2gnuplot: Removing .py extension

It's pretty boring having the .py extension to the tool.
Let's remove it !
fio2gnuplot: Adding manpage

As requested by users, let's add a manpage to make things easier to
understand.

I'm providing here the raw file used to generate the manpage. It can be
converted to a real manpage by using txt2man.

I'm also providing the manpage file to avoid dependencies at build time,
anyway the makefile target can be easily used to rebuild it if
necessary.
genfio: Don't consider only /dev/ disk device

Prior this patch, genfio was considering the disks __NOT__ having the "/dev"
name in it.

That's a serious limitation as
- we can't test regular files
- that doesn't works for complex /dev/ naming like /dev/disk/by-id/...

This patch removes this requirement and let user giving the complete
path.