PluckTuple overwrites regex if used more than once in the same script

If you define two PluckTuples with different regexes, and use them together, they will overwrite the regex field of one another's (this will not affect cases where non-regex prefixes are used).

Example (from testOutput in TestPluckTuple.java, modified)

a = load 'a' using mock.Storage();
b = load 'b' using mock.Storage();
c = join a by x, b by x;
define pluck1 PluckTuple('a::.*');
define pluck2 PluckTuple('b::.*');
d = foreach c generate pluck1 AS pluck1, pluck2 AS pluck2;

Expected:

((1,hey,2),(1,sasf,5))
((2,woah,3),(2,woah,6))

Actual:

((1,sasf,5),(1,sasf,5))
((2,woah,6),(2,woah,6))