It is barely used but cross cuts into most libfirm components and
therefore isn't maintenance free.

The statev framework stays obviously.

Properly use get_irn_pinned/set_irn_pinned as bool value instead of
comparing setting the ir_op enum values.

* No \n at end; panic() adds one
* No punctuation mark at end
* Lowercase first letter

The start block is not special block without any "real" instructions
anymore. In particular this means:

- There is no X_initial_exec Proj from the Start node anymore, "normal"
  cfopts are used for jumping out of the start block.
- The backend never had the special convention of the start block not
  containing actual code and used to fixup this discrpancy, no more
  fixup code needed now.
- The part_block() code got a bit more complicated because splitting the
  start block is tricky (previously part_block() simply failed in this
  case but was never used in the Start block because of its special
  convention)

The previous approach put the irg link into the block attributes, so
while saving memory an extra indirection was necessary. Some testing
with valgrind massif+callgrind revealed that a direct link increses peak
memory usage by ~1% while also increasing runtime by ~1%. More
importantly the code gets a bit simpler and some strange corner cases can be
removed with the direct link.

This commit does:
- Remove tarval_reachable+tarval_unreachable, dataflow analysis rather
  use top/bottom instead of other special values.
- Rename tarval_undefined to tarval_unknown as it corresponds to the
  Unknown node (=a value which we don't know)
- Remove predefined tarval_top/tarval_bottom from tv.h and place the
  defines into combo.c
- Change compute_XXX constant folding functions to return tarval_unknown
  instead of tarval_bad if folding failed
- compute_Unknown in combo results in tarval_bottom == tarval_unknown
  this eliminates strange special cases in the Cond/Switch rules and the
  now unnecessary cprop_X list.

This removes the strange entity/type duality and we get rid of union symconst_symbol.

All users of NEW_ARR_A used it to construct a simple array, yet noone
cared about it actually being an array with a length field in front. For
this simple use case you should use ALLOCAN.

- You can now construct the lookup table separately and perform the
  lowering selectively on irgs (instead of the whole program at once)
  while reusing the lookup table.
- Simplified API a bit.
- Remove i_mapper_RuntimeCall. All users are simpler by doing the
  transformations directly instead of filling in runtime_rt
  structures...

Nobody uses it currently, and it is a burden for everyone writing a new
pass.

They are considered low level operations now which just allocate/free a
block of memory on the stack. There is no highlevel typeinformation
attached anymore or support for heap allocation. Frontends/liboo should
provide their custom highlevel nodes if they need these features.

It has been empty for nearly all systems. People who used to put stuff
in config.h can still create a config.h on their own and inject
-include (gcc) or /FI (msvc) into their CPPFLAGS.

Just state the copyright and the project the files belong to. You can
then find the COPYING file for the whole project.

irgmod: Pass the new inputs to turn_into_tuple() instead of initialising them with Bad and setting them afterwards.

This means floatingpoint calculation in a firm graph must be performed
in the mode specified (and may not be performed in a wider mode as
before).

graph_properties are things that a transformation may destroy but which
can be easily recalculated.

graph_constraints are set after lowering phases have been running and
forbid certain constructs that no (later) transformation is allowed to construct