FELIX-4302 Config Admin can create illegal names on windows

Configuration PIDs are encoded to be used as path names for
configuration files. On Windows platforms each segment in the
path must not start with one of the Windows device special names
such as LPT, COM, etc. Improved the encodePid method to encode
the first character of a segment name if it starts with one of the
special names.

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1554073 13f79535-47bb-0310-9956-ffa450edef68