SI-3452 GenBCode version of the static-forwarder signature fix

Shares the code with the GenASM version of the fix.
adds more tests for enclosingOwners

Makes sure that it's possible to cover sbt's use cases, and also checks
that we can distinguish vals from vars (should anyone ever need that).
adds missing signature of appliedType

Again, thanks to sbt.
Merge pull request #3534 from clhodapp/test/literate_existentials

Add an extremely well-commented test
Merge pull request #3532 from som-snytt/issue/7711

SI-7711 Do not emit extra argv in script body
Merge pull request #3443 from gourlaysama/man-pages

add -Xsource:version to scalac man page
Merge pull request #3527 from Ichoran/issue/8264

SI-8264 scala.collection.immutable.HashSet#- returns broken Set
Merge pull request #3528 from Ichoran/issue/6908

SI-6908 FlatHashTable and things that depend on it can't store nulls
Merge pull request #3511 from som-snytt/issue/interp-octal

SI-8266 Deprecate octal escapes in f-interpolator
Merge pull request #3493 from retronym/ticket/3452-2

SI-3452 Correct Java generic signatures for mixins, static forwarders
Merge pull request #3455 from densh/topic/patdef

Fix SI-8202 and improve support for splicing patterns into vals
Merge pull request #3513 from xeno-by/topic/typecheck-member-defs

typecheck(q"class C") no longer crashes
Merge pull request #3521 from xeno-by/ticket/8270

SI-8270 unconfuses bundles and vanilla macros
Merge pull request #3499 from densh/topic/single-element-tuple

Make handling of tuples more consistent in quasi-quotes
Avoid storing source file contents twice

BatchSourceFile instances contain two almost identical character arrays,
content0 and content. What's worse, content0 is even public. Instead,
content0 should just be a constructor parameter. This seems the residual
of an incomplete refactoring.

I observed this waste of memory during debugging; after applying this
patch, I've verified by hand that the second field indeed disappears.

I don't expect a measurable difference, but this patch is not premature
optimization because it makes code more logical.
Merge pull request #3397 from xeno-by/ticket/5920

SI-5920 enables default and named args in macros
Merge remote-tracking branch 'origin/master' into topic/palladium0

Conflicts:
	src/compiler/scala/reflect/macros/compiler/Resolvers.scala
	src/compiler/scala/reflect/macros/contexts/Typers.scala
	src/compiler/scala/tools/reflect/ToolBoxFactory.scala
	src/reflect/scala/reflect/api/BuildUtils.scala
better deprecation message for Symbol.companionSymbol
SI-6566, unsoundness with alias variance: document fix

Commit a419799f872d5aae99728d711b1ced89e06804a8 changed the behavior of
relativeVariance, but without updating the corresponding comment. Fix
that.
README.md: Add link to CONTRIBUTING.md