Exit Early for Several Commands When A Child Process Fails

[iguessthislldo]

Brought up by OpenDDS#1011 where apt-get install failed so OpenDDS configure script failed but every single other command was run anyway, even though they were all failures. I changed several autobuild commands which create child processes so that they fail when their child processes fail.

Shares some commits with #3 .

[iguessthislldo]

I created a way to try to make this behavior controllable via an XML attribute:

<command name="whatever" required="true"/>

Means that if the command fails, then autobuild stops without processing anymore commands. However I'm not quite sure which way the default should go.

I'm also considering a required tag and/or a optional tag:

<required>
  <command name="build core library"/>
</required>
<optional>
  <command name="build supplement program"/>
  <command name="run test"/>
</optional>

Or maybe a default setting:

<configuration>
<required default="true"/>
</configuration>

[jwillemsen]

The XML attribute is the least intrusive, we have a lot of autobuild xml files. I think the default is to be false, can't really predict what happens when you set the default to true