`task - modify` segfaults

[Impact]
task 2.0 from ubuntu segfaults. See stack trace below.
Fixed upstream: http://taskwarrior.org/issues/1048

[Test Case]
$ task - modify
Segmentation fault (core dumped)

[Fix]
Apport catches the fault but doesn't file a bug report. I reproduced the bug in the current task git tree, and reported it upstream. They've produced a patch, which should be applicable to quantal and precise.

[Trace]
#0 0x00007f0d26f99f88 in std::string::assign(std::string const&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
No symbol table info available.
#1 0x0000000000483311 in operator= (_str=..., this=0x7fff7d77ea10) at /usr/include/c++/4.6/bits/basic_string.h:542
No locals.
#2 Arg::Arg (this=0x7fff7d77ea10, other=...) at /build/buildd/task-2.0.0.release/src/Arg.cpp:79
No locals.
#3 0x0000000000527971 in E9::eval (this=0x7fff7d77ec20, task=..., value_stack=...) at /build/buildd/task-2.0.0.release/src/E9.cpp:122
right = {_value = {static npos = <optimized out>, _M_dataplus = {<std::allocator<char>> = {<_gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, M_p = 0x774cf8 ""}}, _raw = {static npos = <optimized out>, _M_dataplus = {<std::allocator<char>> = {<_gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, M_p = 0x774cf8 ""}}, _type = 2, _category = 0}
result = {_value = {static npos = <optimized out>, _M_dataplus = {<std::allocator<char>> = {<_gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, M_p = 0x774cf8 ""}}, _raw = {static npos = <optimized out>, _M_dataplus = {<std::allocator<char>> = {<_gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, _M_p = 0x774cf8 ""}}, _type = Arg::type_none, _category = Arg::cat_none}
case_sensitive = true
arg = {_M_current = 0x19658f0}

[Regression Potential]
TBD