Code review request: 6907367 extcheck should skip non-jar files

[Xueming Shen]

Please help review the change at

http://cr.openjdk.java.net/~sherman/6907367/webrev

The proposed change does not include the test case I was originally planed
as showed at
http://cr.openjdk.java.net/~sherman/6907367/webrev.00/test/com/sun/tools/extcheck/TestExtcheckArgs.java.sdiff.html

The test case will failed if run against the current jdk8 build image 
because
all those jar files still have their "specification-version" listed as 
"1.7", as

-----------------------------------
Manifest-Version: 1.0
Implementation-Vendor: Oracle Corporation
Implementation-Title: Java Runtime Environment
Implementation-Version: 1.8.0-internal
Specification-Vendor: Oracle Corporation
Created-By: 1.7.0 (Oracle Corporation)
Specification-Title: Java Platform API Specification
Specification-Version: 1.7
------------------------------------

in which case the test case fails when comparing the version.

While I should be able to figure out "where and how" in those release 
makefiles to fix
this, it appears all system jar files will be replaced bye "modules" in 
jdk8 anyway, the
extcheck on system jar files will become much less relevant (as Alan 
suggested). So
I decided to leave the test case out (I did run the test case manually 
to verify the fix).

Thanks,
Sherman