Add version to -Xmigration

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$ scala -version
Scala code runner version 2.10.0 -- Copyright 2002-2012, LAMP/EPFL

# yay!!

$ scala -X
...
  -Xmigration                    Warn about constructs whose behavior may have changed between 2.7 and 2.8.

# wat?

Adding a version number argument should clean that up

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6963?orig=1
Reporter: @JamesIry
Assignee: @JamesIry
Affected Versions: 2.9.3-RC1, 2.10.0

[scabug]

@soc said:
Earlier attempts:

https://groups.google.com/forum/#!searchin/scala-internals/%E2%80%9C-Xmigration%E2%80%9D/scala-internals/5fIw3w4LJbU/d3myzRFk23gJ

scala/legacy-svn-scala#91

scala/scala#49

https://groups.google.com/forum/#!searchin/scala-internals/migration/scala-internals/SPxf0gPPtvs/eaovZ90ZtR8J

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@JamesIry said:
scala/scala#1895

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@JamesIry said:
The deprecation is now in 2.10.x. To avoid a merge conflict I'll wait until that's in master and then remove the entire switch.

[scabug]

@JamesIry said:
scala/scala#1922

[scabug]

@JamesIry said:
New plan is to add a version parameter to -Xmigration in 2.11. Then it would only print a warning on things that changed after that version number.

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@JamesIry said:
scala/scala#1998