added Edges class to consolidate code operating on set of input or successor edges and to better isolate magic used to access edges

--HG--
rename : graal/com.oracle.graal.compiler.test/src/com/oracle/graal/compiler/test/NodeRefIteratorTest.java => graal/com.oracle.graal.compiler.test/src/com/oracle/graal/compiler/test/NodePosIteratorTest.java
rename : graal/com.oracle.graal.replacements/src/com/oracle/graal/replacements/NodeClassSubstitutions.java => graal/com.oracle.graal.replacements/src/com/oracle/graal/replacements/EdgesSubstitutions.java
Enforce catch-blocks for Debug.Scopes with context objects.

--HG--
extra : rebase_source : 6697cb7a4de51ca8375ad051aeedf4fd43cdf1ec
ConstantLoadOptimization: make debug meters final.