Add uplevel keyword to Kernel#warn and use it

If uplevel keyword is given, the warning message is prepended
with caller file and line information and the string "warning: ".
The use of the uplevel keyword makes Kernel#warn format output
similar to how rb_warn formats output.

This patch modifies net/ftp and net/imap to use Kernel#warn
instead of $stderr.puts or $stderr.printf, since they are used
for printing warnings.

This makes lib/cgi/core and tempfile use $stderr.puts instead of
warn for debug logging, since they are used for debug printing
and not for warning.

This does not modify bundler, rubygems, or rdoc, as those are
maintained outside of ruby and probably wish to remain backwards
compatible with older ruby versions.

rb_warn_m code is originally from nobu, but I've changed it
so that it only includes the path and lineno from uplevel
(not the method), and also prepends the string "warning: ",
to make it more similar to rb_warn.

From: Jeremy Evans code@jeremyevans.net
Signed-off-by: Urabe Shyouhei shyouhei@ruby-lang.org


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61155 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rexml/instruction.rb

@@ -43,7 +43,7 @@ module REXML
     # See the rexml/formatters package
     #
     def write writer, indent=-1, transitive=false, ie_hack=false
-      Kernel.warn( "#{self.class.name}.write is deprecated" )
+      Kernel.warn( "#{self.class.name}.write is deprecated", uplevel: 1)
       indent(writer, indent)
       writer << START.sub(/\\/u, '')
       writer << @target