[vala] (25 commits) Non-fast-forward update to branch wip/baedert/nullable

[Timm Bäder <baedert src gnome org>]

The branch 'wip/baedert/nullable' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  8e49cbb... datatype: Properly mark generic types nullable

Commits added to the branch:

  64b72f3... method: Print encountered type if return types mismatch
  1520be1... memberaccess: Don't check for nullability
  1c52403... basicblock: Add per-block name
  d1141f2... basicblock: Save per-block null/non-null symbols
  2c15aeb... Add nullability checker
  617d71f... add some nullability tests
  8cf8082... add AstPrinter
  aec692d... symbolresolver: Don't assume all locals are nullable
  fac6e6c... nullabilitychecker: Warn on invalid assignments
  0bdd197... binaryexpression: Fix is_non_null for COALESCE expressions
  9d555d1... glib-2.0: unichar.to_string doesn't return null
  2955e29... astprinter: Print binary expressions
  85c3bbd... astprinter: Don't print null initializers
  f56fae5... expression: Add get_null_state vfunc
  058666b... flowanalyzer: Add helper to query visible version of variab
  f4ffbaa... astprinter: Improve assignment output
  ef563c0... basicblock: Add names for entry() and exit() blocks
  7ad962f... compiler: Print ast after checking
  b010635... Add more nullability tests
  80c2445... astprinter: Print nullability state of binary expression
  eba833a... astprinter: Remove unused function
  14b9a54... astprinter: Fix assignment printing
  658d389... tests: Add another nullability test
  08849bb... checkpoint
  7e6baf0... WIP