Implement MySqlCommand.Prepare

[bgrainger]

MySqlCommand.Prepare is currently unimplemented:

1. Only a subset of statements are actually preparable by the server: http://dev.mysql.com/worklog/task/?id=2871
2. Although CLIENT_MULTI_STATEMENTS is supposed to mean that the Server "Can handle multiple statements per COM_QUERY and COM_STMT_PREPARE" (https://dev.mysql.com/doc/internals/en/capability-flags.html#flag-CLIENT_MULTI_STATEMENTS), this is not actually true because "Prepared statement handles are defined to work only with strings that contain a single statement" (http://dev.mysql.com/doc/refman/5.7/en/c-api-multiple-queries.html).

Connector/NET has a IgnorePrepare connection string setting that defaults to true; unless the user explicitly sets that to false then its Prepare method also does nothing.

• Determine how best to handle Prepare (e.g., accept the client's SQL as-is and let them be responsible for knowing server's limitations; or, break the command into individual statements, divide up the parameters and prepare them individually).
• Determine if IgnorePrepare option should be supported, and its default value

[bgrainger]

Add MySqlCommand.IsPrepared.

[bgrainger]

#534 adds initial support: single statements, no stored procedures.

[bgrainger]

Determine how best to handle Prepare (e.g., accept the client's SQL as-is and let them be responsible for knowing server's limitations; or, break the command into individual statements, divide up the parameters and prepare them individually).

Will do the latter (breaking the command up into individual statements); however, the client will still need to be aware of statements that can be prepared.

Determine if IgnorePrepare option should be supported, and its default value

It will be supported, and default to true (same as Connector/NET).

[bgrainger]

Prepare has been implemented for single commands for a while, and is now implemented for multiple commands as part of MySqlBatch (#650) in 0.57.0.