This implements the dotfile idea from jruby#5824 in our bash launcher.
The order of precedence for options, indicated by their position
in the java command line, goes as follows:
* home dir .jruby.java_opts
* current dir .jruby.java_opts
* JAVA_OPTS environment variable
* command line flags
This allows users to set up global, local, and environment-based
java options but still override those at the command line.
An equivalent change will need to go into jruby-launcher.