Previously, xpath() simply returned an empty array if the expression did
not yield a node set. This is useless for expressions that return scalars,
such as one with name() at the top level. Arrange to return the scalar
value as a single-element xml array, instead. (String values will be
suitably escaped.)
This change will also cause xpath_exists() to return true, not false,
for such expressions.
Florian Pflug, reviewed by Radoslaw Smogura
0ce7676aa0