RFR 8142367: Allow files with .png extension to be copied for javadoc

[Bhavesh Patel]

Hi,
  As a part of javdoc search feature for JDK 9 (JEP 225. JIRA: https://bugs.openjdk.java.net/browse/JDK-8142367), javadoc would need to copy files with .png extension to the generated output folder. the langtools/make/CompileInterim.gmk needs to be updated to allow .png files. Currently, only .gif image files are supported.

JIRA: https://bugs.openjdk.java.net/browse/JDK-8142367
Webrev: http://cr.openjdk.java.net/~bpatel/8142367/webrev.00/webrev

Regards,
Bhavesh.