RFR: 8283287: ClassLoader.c cleanups [v4]

[Tyler Steele]

> As mentioned in the issue, I'd like to perform the following tidying on ClassLoader.c
> 
> - Alphabetize includes.
> - Replace 'if (ptr == 0)' with 'if (ptr == NULL)'.
> - Replace 'return 0' with 'return NULL'.

Tyler Steele has updated the pull request incrementally with one additional commit since the last revision:

  Removes offending whitespace

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7846/files
  - new: https://git.openjdk.java.net/jdk/pull/7846/files/d7e67d4c..2fd5b368

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7846&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7846&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7846.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7846/head:pull/7846

PR: https://git.openjdk.java.net/jdk/pull/7846