avoid creating include as file

[DJ Delorie]

> Why didn't the touch fail then?

It did, but the error message wasn't obvious enough for me to grasp
the true problem right away.  So did the rm fail, but quietly.  Then
the cp created the file "include", no error.  On the second pass, the
touch failed again - with a different error, which was even less
obvious.

My change just changes one of the errors from a non-obvious error to
an obvious error, and prevents "include" from being created as a file.