RFR [8042990] Optimize conversion to hex string

[Ivan Gerasimov]

Hello!

There is a method Integer.toHexString(int), which produce a string with 
no extra leading zeroes.
I found a couple of places in jdk, where it would be useful to have a 
variant of the method which pads the result with the required amount of 
zeroes.

Would you please take at the webrev?
http://cr.openjdk.java.net/~igerasim/8042990/0/webrev/

It includes implementations of Integer.toHexString(int, int) and 
Long.toHexString(long, int) with the second argument standing for the 
minimum width of the produced string.
It also contains a few replacements of the same behaving code with calls 
to these new methods.

Sincerely yours,
Ivan