rename zero_elm -> zero in DegreesOfEntriesFunction
predefine weights in NonTrivialDegreePerColumnWithRowPositionFunction
fixed bug in NonTrivialDegreePerRowWithColPositionFunction

by removing the local declaration of zero
modified the tool method Diff

- the tool method Diff now expects RP!.Diff( D, N ) to return matrices
  (I also allowed IshomalgExternalObjectRep as output not to be forced
   to rewrite the homalgTable entries for Singular and Macaulay2)
- adapted CommonHomalgTableForGradedRingsTools accordingly

this avoids a bug when localizing a graded ring R as HomalgMatrix
gets automatically called in ConstructorForHomalgMatrices( R )
before MatrixOverGradedRing is called; I observed this bug
when localizing divisors over Proj (for the collaboration with Paco)
installed RingOfDerivations for [ IsHomalgGradedRingRep ]

using the new single argument method in MatricesForHomalg v2012.05.25
Merge branch 'devel' into gutsche

* devel:
  installed RingOfDerivations for [ IsHomalgGradedRingRep ]
  modified the tool method Diff

Conflicts:
	PackageInfo.g
	gap/GradedRing.gi
Fixed a small error.
Merge pull request #9 from sebasguts/master

Vielen Dank Stebastian, gute Arbeit
added Sebastian as author in the manual
fixed WeightsOfIndeterminates for [ IsHomalgGradedRing and HasAmbientRing ]

now it saves its result
the graded ring constructor GradedRing now does not SetRingRelations

this is now done in \/ for [ IsHomalgGradedRingRep, IsHomalgRingRelations ]

+ fixed DegreeOfRingElementFunction for [ IsHomalgGradedRing and HasAmbientRing ]
fixed MatrixOfWeightsOfIndeterminates in Macaulay2Tools.gi
fixed MatrixOfWeightsOfIndeterminates in SingularTools.gi
outsourced DegreeOfRingElement to lower level packages

outsourced
- HOMALG_IO.Pictograms.DegreeOfRingElement -> HomalgToCAS v2012.06.27
- GradedRingMacrosFor*.DegreeOfRingElement -> RingsForHomalg v2012.06.27
- GradedRingTableFor*Tools.DegreeOfRingElement -> RingsForHomalg v2012.06.27
comply with the new GAPDoc testing methods
fixed GradedRingTableForSingularTools entry WeightedDegreesOfEntries
NonTrivialDegreesPerRow/Column for empty matrices (barely tested)
updated manual.css
W  PackageDoc.Archive is withdrawn, use PackageDoc.ArchiveURLSubset instead
added Diff to GradedRingMacrosForMAGMA

and activated it in GradedRingTableForMAGMATools