Making parse_config accepts a String like Ruby MRI

[edipofederle]

With Ruby MRI, we can do:

OpenSSL::Config.parse_config("") # also accepts a String

but not with JRuby:

NoMethodError: undefined method `lineno' for "":String
   Did you mean?  lines

[edipofederle]

@kares maybe we can take a quick look into this one? thanks

[headius]

Seems like this is ready to go?

[kares]

did look into this but did not figure out a path fwd. the logic isn't matching what MRI is doing (in native C)...

• parse isn't calling parse_config (we're a bit convoluted here parse -> parse_config -> parse)
• check is done on having an IO-like (gets ugly with JRuby) and everything else is considered io.to_str

@headius but if it looks good to you, feel free to merge.
I usually "Squash and merge" small change-sets (easier to dig out history) but if you have a different preference it's fine