#9907: call rl_initialize early when using editline on OSX
editline rl_initialize apparently discards any mappings done before it
is called, which makes tab revert to file completion instead of inserting
a tab. So now on OSX we call rl_initialize first if we are using
readline, and then re-read the users .editrc (if any) afterward so they
can still override our defaults.
Patch by Ned Deily, modified by Ronald Oussoren.
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