Updating to latest ycmd

Since ycmd doesn't need 'query', 'start_column' and 'line_value' params, we
don't send them anymore.
Updating to latest ycmd
OmniCompleter requests now have buffer data

RequestWrap needs buffer data to produce computed properties.
Refactored completion request creation

- OmniCompleter is now more similar to other Completers.
- CompletionRequest doesn't store start_column anymore.
- Calling BuildRequestData only once per request.
Fix missing param in OmniCompletionRequest
Removing erroneous whitespace
Updating to latest ycmd
Better detection of shortmess 'c' availability

Also noting that the annoying messages during completion go away with Vim
7.3.314.

Related to #642.
Minor rewording in README
add g:ycm_diagnostic_ignore_files option

Use this option to specify files that do not display diagnostic UI. It's
a list of regular-expression patterns. The full paths of files are
matched against these patterns, and the matches are case sensitive.

This option is part of the Syntastic compatibility layer; if the option
is not set, YCM will fall back to the value of the
`g:syntastic_ignore_files` option before using this option's default.