Incorrect use of delete[] in ptr_rep

[Paul J. Lucas]

test/libunit/string

 ==28568== Mismatched free() / delete / delete []
==28568== at 0x4C26A4B: operator delete[](void*) (vg_replace_malloc.c:409)
==28568== by 0x5EED144: zorba::rstring<zorba::rstring_classes::ptr_rep<zorba::atomic_int, std::char_traits<char>, std::allocator<char> > >::~rstring() (ptr_rep.h:321)
==28568== by 0x5EE8969: void test_non_empty<zorba::rstring<zorba::rstring_classes::ptr_rep<zorba::atomic_int, std::char_traits<char>, std::allocator<char> > > >(zorba::rstring<zorba::rstring_classes::ptr_rep<zorba::atomic_int, std::char_traits<char>, std::allocator<char> > >&, char const*) (string.cpp:136)
==28568== by 0x5EE8D33: void test<zorba::rstring<zorba::rstring_classes::ptr_rep<zorba::atomic_int, std::char_traits<char>, std::allocator<char> > > >() (string.cpp:152)
==28568== by 0x5EEAA9A: zorba::UnitTests::test_string(int, char**) (string.cpp:792)
==28568== by 0x5EF5BCF: zorba::UnitTests::runUnitTest(int, char**) (unit_tests.cpp:72)
==28568== by 0x400BAC: main (lib_unit_test.cpp:34)
==28568== Address 0xaac7d70 is 0 bytes inside a block of size 6 alloc'd
==28568== at 0x4C27CC1: operator new(unsigned long) (vg_replace_malloc.c:261)
==28568== by 0x5EE83B8: void test_non_empty<zorba::rstring<zorba::rstring_classes::ptr_rep<zorba::atomic_int, std::char_traits<char>, std::allocator<char> > > >(zorba::rstring<zorba::rstring_classes::ptr_rep<zorba::atomic_int, std::char_traits<char>, std::allocator<char> > >&, char const*) (string.cpp:93)
==28568== by 0x5EE8D33: void test<zorba::rstring<zorba::rstring_classes::ptr_rep<zorba::atomic_int, std::char_traits<char>, std::allocator<char> > > >() (string.cpp:152)
==28568== by 0x5EEAA9A: zorba::UnitTests::test_string(int, char**) (string.cpp:792)
==28568== by 0x5EF5BCF: zorba::UnitTests::runUnitTest(int, char**) (unit_tests.cpp:72)
==28568== by 0x400BAC: main (lib_unit_test.cpp:34)