The javadoc task fails if
- useexternalfile="true" is used, and
- the Java source files contain white space somewhere in there path names.

Since Javadoc sees the file submitted on the command line via "javadoc
@argsfile" as a file containing a list of arguments and not as a list of files
with each file name on a separate line, it is correct in interpreting white
space in a file name as an argument separator.

I helped myself by surrounding the file names by single quotes and by doubling
all backslashes. (The latter I had to do since I am forced to work under Windoze
NT. :-()

Ant's javadoc task should quote the file names correctly when generating the
external file list.