JavaProxySearchStrategy only enabled with HTTP system properties given

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What steps will reproduce the problem?

1. specify HTTPS, FTP, ... java proxy properties only, but no HTTP ones
2. try to use the JavaProxySearchStrategy


What is the expected output? What do you see instead?

expected: non-null ProxySelector instance returned from 
JavaProxySearchStrategy#getProxySelector()

actual: null due to #proxyPropertyPresent() method testing only for HTTP proxy 
system properties.


What version of the product are you using? On what operating system?

20131209


Please provide any additional information below.

This should be a rare problem. Happened for me only while testing and being 
lazy for system properties specification then, I knew that there will be only 
HTTPS accesses.

Original issue reported on code.google.com by [e-mail] on 2 Apr 2015 at 3:27