If no mergetool is configured in the configuration variable
merge.tool the resetting message should not be printed.
This is fixed. The message is only printed if a tool is configured
but the entry in merge.tool is invalid.
Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>