Fix to crashes when running with Coreutils

[domainexpert]

This fixes crashes with the following message when running with Coreutils (e.g., executing make dirname.tx in coreutils directory of klee-examples repository).

klee: TxStore.cpp:161: bool klee::TxStore::isInLeftSubtree(uint64_t) const: Assertion `current->depth > targetDepth && "entry should have been defined in an ancestor node"' failed.
0  libLLVM-3.4.so.1 0x00007fa0b351e042 llvm::sys::PrintStackTrace(_IO_FILE*) + 34
1  libLLVM-3.4.so.1 0x00007fa0b351de34
2  libpthread.so.0  0x00007fa0b2423390
3  libc.so.6        0x00007fa0afbc2428 gsignal + 56
4  libc.so.6        0x00007fa0afbc402a abort + 362
5  libc.so.6        0x00007fa0afbbabd7
6  libc.so.6        0x00007fa0afbbac82
7  klee             0x00000000004f640b
8  klee             0x00000000004cc41f klee::TxStoreEntry::TxStoreEntry(klee::ref<klee::TxStateAddress>, klee::ref<klee::TxStateValue>, klee::ref<klee::TxStateValue>, klee::TxStore const*, unsigned long) + 863
9  klee             0x00000000004f77d3 klee::TxStore::MiddleStateStore::updateStore(klee::TxStore const*, klee::ref<klee::TxStateAddress>, klee::ref<klee::TxStateValue>, klee::ref<klee::TxStateValue>, unsigned long) + 227
10 klee             0x00000000004f84e8 klee::TxStore::updateStore(klee::ref<klee::TxStateAddress>, klee::ref<klee::TxStateValue>, klee::ref<klee::TxStateValue>) + 408
11 klee             0x00000000004dc13b klee::Dependency::execute(llvm::Instruction*, std::vector<llvm::Instruction*, std::allocator<llvm::Instruction*> > const&, std::vector<klee::ref<klee::Expr>, std::allocator<klee::ref<klee::Expr> > >&, bool) + 4507
12 klee             0x00000000004dee97 klee::Dependency::executeMemoryOperation(llvm::Instruction*, std::vector<llvm::Instruction*, std::allocator<llvm::Instruction*> > const&, std::vector<klee::ref<klee::Expr>, std::allocator<klee::ref<klee::Expr> > >&, bool, bool) + 71
13 klee             0x0000000000482b2e klee::TxTree::executeMemoryOperation(llvm::Instruction*, klee::ref<klee::Expr>, klee::ref<klee::Expr>, bool) + 206
14 klee             0x000000000047722e klee::Executor::executeMemoryOperation(klee::ExecutionState&, bool, klee::ref<klee::Expr>, klee::ref<klee::Expr>, klee::KInstruction*) + 4126
15 klee             0x0000000000478cab klee::Executor::executeInstruction(klee::ExecutionState&, klee::KInstruction*) + 2875
16 klee             0x000000000047eca9 klee::Executor::run(klee::ExecutionState&) + 1689
17 klee             0x000000000047f6c8 klee::Executor::runFunctionAsMain(llvm::Function*, int, char**, char**) + 1672
18 klee             0x00000000004581e0 main + 12688
19 libc.so.6        0x00007fa0afbad830 __libc_start_main + 240
20 klee             0x0000000000460759 _start + 41

With this patch, make check succeeded 100% and make in klee-examples basic did not result in change in subsumption and error counts.