Draft 9: Rename ExecutionType to ExecutionModeType.

[Gary P Cole <Gary.P.Cole@Sun.COM>]

We should do the following:
1) Rename "ExecutionType" to "ExecutionModeType".
2) Rename the "execution" attribute of SpmlRequestType to "executionMode".
3) Replace the 'unsupportedExecutionType' value of ErrorCode to 
'unsupportedExecutionMode'.

Reasons:
1) Almost everything in our schema with a name that ends in "Type" *is* 
a type.
    ExecutionType and ChangeType are the only exceptions.
2) "executionMode" is clearer and more specific than "execution".
3) "unsupportedExecutionMode" is clearer than "unsupportedExecutionType"
    and avoids the term "Type" which is heavily overloaded in XML Schema.

gpc