Add hooks for generic command execution

pre-command and post-command will always be executed before and after
any command is being executed. This does not affect inner calls.

vcsh

@@ -283,5 +283,7 @@ done
 
 verbose "$VCSH_COMMAND begin"
 export VCSH_COMMAND=$(echo $VCSH_COMMAND | sed 's/-/_/g')
+hook pre-command
 $VCSH_COMMAND
+hook post-command
 verbose "$VCSH_COMMAND end, exiting"