Improve socket exception message when bind() fails
If the user tries to bind a port that is already in use the user does not receive any notification of which port (and address) failed. When multiple connections are being made makes it difficult to determine which connection was not correctly bound.
For example, WEBrick binds both IPv4 and IPv6 sockets. If one of the ports is already bound you will receive a confusing error message.
This patch adds the port and address to the error message:
$ cat test.rb
TCPServer.new '0.0.0.0', 5900
$ make runruby
./miniruby -I./lib -I. -I.ext/common ./tool/runruby.rb --extout=.ext -- --disable-gems ./test.rb
initialize': Address already in use - bind(2) for "0.0.0.0" port 5900 (Errno::EADDRINUSE)new'
from ./test.rb:3:in `'
make: *** [runruby] Error 1
$ ruby test.rb
initialize': Address already in use - bind(2) (Errno::EADDRINUSE)new'
from test.rb:3:in `'