Fixing GEXF parsing in IE.

IE apparently doesn't support getElementsByTagNameNS for XML documents.
if edge weight is set, set size attribute to this value to make setting minEdgeSize and maxEdgeSize effective
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'fix-ie-gexf/fix-ie-gexf' into devel
Merge remote-tracking branch 'parse-json/parseJSON' into devel
add interpreter command
make sure attr is in nodesAttributesDict
edge ids can be duplicate in gexf exports of directed graphs, thus do not use the gexf edge id but increment a counter same as in parseGexf plugin
Merge pull request #7 from yaph/devel

ie parseGexf fix, parseJson use unique edgeId, python fix for attributes not in dict. Thanks, yaph.