Pending test for SI-5459.
Renames normalize to normalizeModifiers.

Since we still have too many methods called normalize.
Changes many calls to normalize to dealiasWiden.

Calling normalize is very aggressive and is usually the wrong
thing. It is one of the leading contributors to non-determinism
in compiler outcomes (often of the form "I gave a debugging or
logging compiler option and it started/stopped working") and
should be used only in very specific circumstances.

Almost without exception, dealiasWiden is what you want; not
widen, not normalize. If possible I will remove normalize from
Type entirely, making it private to those areas of the compiler
which actually require it.
Expanded the comment on Type#normalize.

As suggested by reviewer.
Fix access to empty package from the repl.

It seems that way back in f5c336d566 three months ago I
booched the repl's ability to get at the empty package.
I've noticed this a hundred times but strangely it has not
been reported by anyone else. Perhaps you are all religious
package users. In any case, it is back.
Overhaul of tools/partest-ack.

I decided what would be really handy for test selection is
being able to run all the tests which were created or modified
at the same time as something else. Right now that is at file
granularity, though it would be simple enough to generalize it
such that any expression which can be translated to a set of
git commits can also be turned into a selection of tests.

I added some other options as well:

Usage: $0 <regex> [-dfquvp] [ack options]

  -d          pass --debug to partest
  -f          pass --failed to partest
  -q          DON'T pass --show-log and --show-diff to partest
  -u          pass --update-check to partest
  -v          pass --verbose to partest
  -p <path>   select tests appearing in commits where <path> was also modified

Example usage:

  > tools/partest-ack -p src/compiler/scala/tools/nsc/typechecker/Checkable.scala
  % tests-modified-in-same-commit  ...  12
  # 12 tests to run.
  Testing individual files
  testing: [...]/files/pos/t6537.scala                                  [  OK  ]

  Testing individual files
  testing: [...]/files/neg/unchecked-impossible.scala                   [  OK  ]
  testing: [...]/files/neg/t1872.scala                                  [  OK  ]
  testing: [...]/files/neg/t4302.scala                                  [  OK  ]
  testing: [...]/files/neg/unchecked-knowable.scala                     [  OK  ]
  testing: [...]/files/neg/unchecked-abstract.scala                     [  OK  ]
  [etc]
Merge pull request #2013 from paulp/pr/normalize-less

Changes many calls from normalize to dealiasWiden.
Merge pull request #2045 from paulp/pr/partest-ack

Overhaul of tools/partest-ack.
Merge pull request #2027 from paulp/pr/fix-empty-package

Fix access to empty package from the repl.