In convert/resize mode a backup can be created if the new file name
is not specified or the same as the source file name. In commit mode
both base image and redolog file are affected by the backup switch.
Added Linux specific file copy code using '/bin/cp'.
- added support to use 'concat' and 'dll' mode images as convert source.
A prefix ("concat:" or "dll:") must be added to the path since autodetection
doesn't work for these modes.
- create: fixed virtual disk size calculation based on C/H/S
- convert / resize (interactive mode): use original filename as the template for
the new one if not specified on the command line
