Move error_number and sql_state into Mysql2::Error initializer

[sodabrew]

An alternative to #544, make all of the needed parameters into the initialize method.

[simi]

Is there any situation when user should raise Mysql2:Error manually?

[sodabrew]

I don't think so. But it does change the interface away from StandardError, which only takes one argument. Alternatively, add a second constructor, e.g. new_with_sql_state.

Edit: server_version is already an extra argument beyond StandardError.

[simi]

Current implementation differs from StandardError constructor also.
http://www.ruby-doc.org/core-2.1.2/Exception.html#method-c-new (1 optional - msg)
def initialize(msg, server_version=nil) (1 mandatory, 1 optional)

[sodabrew]

@seuros I don't think changing the initialize method is a problematic change, because the arguments are very new. server_version was added in 271ea5e in January 2014 for version 0.3.15.

That said, I further modified the PR to move server_version and the other args into new_with_args. Let me know what you think of this approach.

Ideally, this is where we would use a separate exception class. For 0.4 perhaps.

[simi]

I'm still not getting the idea behind new_with_args. Compatibility trade-off?

[sodabrew]

Sort of a thought experiment, since the extra args are only used by one caller in client.c, and don't really fit a getter/setter pattern because the args are only added at initialization.=

[seuros]

I will have to check tomorrow my logs, I think it was some gem that raised this error when a deadlock is detected.
Fell free to merge this PR , then yours. We can always return to this change in case we break too many implementation?

We should also think about a major version bump, so we can remove all the legacy code. wdyt ?

[sodabrew]

Yes, I'm planning for 0.4 "soon", after a 0.3.17 bugfix release.

[sodabrew]

I was also hoping this would fix #641 but it's still busted with:

  1) Mysql2::Error encoding returns error messages and sql state in Encoding.default_internal if set

     Failure/Error: client.query(valid_utf8)
     LoadError:
       dlopen(e, 9): image not found - e
     # ./lib/mysql2/error.rb:27:in `encode'
     # ./lib/mysql2/error.rb:27:in `new_with_args'
     # ./lib/mysql2/client.rb:87:in `_query'
     # ./lib/mysql2/client.rb:87:in `block in query'
     # ./lib/mysql2/client.rb:86:in `handle_interrupt'
     # ./lib/mysql2/client.rb:86:in `query'
     # ./spec/mysql2/error_spec.rb:31:in `block (3 levels) in <top (required)>'
     # ./spec/mysql2/error_spec.rb:76:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:19:in `with_internal_encoding'
     # ./spec/mysql2/error_spec.rb:75:in `block (3 levels) in <top (required)>'