Wrap automatically non-dgsh compatible commands

[mfragkoulis]

Have the bash shell check whether a command is dgsh compatible when processing a dgsh pipeline. If it isn't compatible, prepend dgsh-wrap to the command for execution. As a result, bash will invoke dgsh-wrap which will first engage in a dgsh negotiation and then exec the passed command.

[dspinellis]

Check for the following to determine if a file is dgsh compatible

• First line contains the dgsh-wrap
• First line contains env dgsh
• Executable defines the global text symbol dgsh_negotiate (found in the output of nm and cached).

[dspinellis]

When done remove all the wrapped commands that have default I/O requirements.