Add method to get all_contracts key in solidity

Author: LefterisJP

ethereum/_solidity.py

@@ -272,6 +272,17 @@ def solidity_get_contract_data(all_contracts, filepath, contract_name):
     return contract_data
 
 
+def solidity_get_contract_key(all_contracts, filepath, contract_name):
+    """ A backwards compatible method of getting the key to the all_contracts
+    dictionary for a particular contract"""
+    if contract_name in all_contracts:
+        return contract_name
+    else:
+        _, filename = os.path.split(filepath)
+        contract_key = filename + ":" + contract_name
+        return contract_key if contract_key in all_contracts else None
+
+
 def compile_contract(filepath, contract_name, libraries=None, combined='bin,abi', optimize=True, extra_args=None):
     all_contracts = compile_file(
         filepath,