RFR: [15] JDK-8245696 javadoc crashes when a doc-files directory contains a '#' file

[Jonathan Gibbons]

Please review a simple fix to prevent javadoc crashing when it 
encounters a badly-named
file in a doc-files subdirectory.

The problem is caused by checks in JavaFileManager causing 
IllegalArgumentException
to be thrown. Rather than catch those exceptions, the files in the 
doc-files source
directory are checked with similar checks, so that a warning can be 
given and the
files ignored.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8245696
Webrev: http://cr.openjdk.java.net/~jjg/8243113/webrev.00/