Merge pull request #45 in G/fastr from ~LUKAS.STADLER_ORACLE.COM/fastr:bugfix/various_changes3 to master

* commit '3bbeee17':
  copyright fixes
  R_NaString is a CHARSXP

Merge pull request #46 in G/fastr from ~ADAM.WELC_ORACLE.COM/fastr:feature/mlr_package_load to master

* commit 'f64bd193':
  Parse shouldn't automatically wrap result in RLanguage object.

Merge pull request #43 in G/fastr from ~MICK.JORDAN_ORACLE.COM/fastr:bugfix/modeltools-install to master

* commit '622ae26b':
  add stats4 package; fix DOTSXP serialization bugs

Merge pull request #44 in G/fastr from ~LUKAS.STADLER_ORACLE.COM/fastr:feature/post_merge_gate to master

* commit '66686d10':
  add gate runs "post-merge"

Merge pull request #41 in G/fastr from ~LUKAS.STADLER_ORACLE.COM/fastr:bugfix/various_changes3 to master

* commit '1c0d50c6':
  fix atanh builtin
  profile in FunctionDefinitionNode (whether ReturnException depth matches)
  simplify printing Utils

* commit 'bdce4250':
  Fix compile error

Merge pull request #38 in G/fastr from ~STEPAN.SINDELAR_ORACLE.COM/fastr:GR-131-remove-rdataframe to master

* commit '29ec23f3':
  Fix data frame tests
  Fix header in TestBuiltin_extract_dataframe
  Add extract data frame test expected outputs
  Remove unused RDataFrame related parameter from setVectorClassAttr
  create InheritsCheckNode in Bind
  Removed leftover commented code.
  Removed RDataFrame and remaining references to it.
  Removed data.frame specific code from CachedVectorNode
  Removed RDataFrame specific code from RSerialize
  Removed simple usages of RDataFrame
  Vector does not turn itself into RDataFrame

Merge pull request #39 in G/fastr from ~ADAM.WELC_ORACLE.COM/fastr:feature/r_caller_overhaul to master

* commit 'da57ed19':
  Folded RSyntaxNodeWrapper interface into (now also an interface) RCaller.
  Invalid caller is now a singleton.
  Fixed a copyright check.
  Regenerated tests.
  Traversing parent hierarchy in search for RCaller is no longer necessary at all and RCaller now has a typed representation.
  The mget function can now use functions as ifnotfound argument.
  Traversing parent hierarchy in search for RCaller is no longer necessary for call nodes.
  Fixed a caller of function called via do.call.
  Partial fix to the sys.call problem in the context of S3/S4.

Merge pull request #40 in G/fastr from ~LUKAS.STADLER_ORACLE.COM/fastr:bugfix/update_truffle to master

* commit '28624ea1':
  ignore warning context for lgamma test
  update Truffle dependency

Traversing parent hierarchy in search for RCaller is no longer necessary at all and RCaller now has a typed representation.

Added several unit tests for [.data.frame, which is the only function
from data.frame specific versions of [[, [, [[<-, [ that calls NextMethod,
i.e. transfers the control to CachedVectorNode

Removed RClass enum introduced in one of the previous commits,
for the time being the "data.frame" literal lives only in RRuntime
class together with static helper hasRClass

Also removed SEXPTYPE.FASTR_DATAFRAME, which was used only internally.
Data frames are serialized as any other RList.