Add PropertyCheckConfiguration which uses anyvals, and deprecate PropertyCheckConfig.   (Uses PosX.from factory methods, because "you cannot use macro implementations in the same compilation run that defines them".  If scalactic were in a separate compile, this would go away.)
Adapt PropertyCheckConfigSuite into PropertyCheckConfigurationSuite.
Add maxDiscardedFactor factory method and tests.
Change non-deprecated PropertyCheckConfigParam classes to use anyvals.
Ensure all references to PropertyCheckConfig -> PropertyCheckConfiguration and update documentation.
Add SizeRange and sizeRange, deprecating MaxSize and maxSize.
Use private[scalatest] fields for legacy param values.
Separate out PropertyCheckConfigurationHelperSuite.
Fix GenGen compile errors.

TODO: Try to find a smoother upgrade path---compile errors would likely not indicate to a user that this change was required.  Example error message:
[error] /Users/broberts/Documents/workspace/scalatest/gentests/GenGen/target/scala-2.11/src_managed/test/scala/gengen/GeneratorDrivenPropertyChecksMixinSuite.scala:702: could not find implicit value for parameter config: GeneratorDrivenPropertyChecksMixinSuite.this.PropertyCheckConfiguration
[error]     forAll { (a: String) =>
[error]            ^
Add failing test for backwards compatability of PropertyCheckConfig -> PropertyCheckConfiguration change.  See ConfigImplicitOverrideInClassTest.
Add PropertyCheckConfigurable trait, common to both PropertyCheckConfiguration and deprecated PropertyCheckConfig.  This allows more seamless upgrades.  See fixed ConfigImplicitOverrideInClassTest for an example where this is necessary.
Use macro versions of PosDouble, PosInt, and PozInt, now possible due to scalactic-macros project being separated out in #457