WL#6978: Deprecate unique option prefixes

Affects: Server-5.7   —   Status: Complete   —   Priority: Medium

http://dev.mysql.com/doc/refman/5.6/en/program-options.html says:
"An option can be specified by writing it in full or as any unambiguous prefix. 
For example, the --compress option can be given to mysqldump as --compr, but not 
as --comp because the latter is ambiguous.
Be aware that the use of option prefixes can cause problems in the event that new 
options are implemented for a program. A prefix that is unambiguous now might 
become ambiguous in the future.

This behavior is confusing and non-future proof in its basic form.
Adding extra options through plugins causes option prefixes in scripts to be 
unreliable even across server restarts.
It also "pollutes" the server options namespace and leaves very little "available" 
options to new plugins.

This worklog aims to deprecate unique prefixes and only accept full option names.

Update: Original implementation deprecated this feature in 5.7 (added warnings). 
Revised implementation deprecated this feature in 5.5, 5.6 (added warnings) and 
removed the feature in 5.7.

User Documentation