qca2: Patch for gcc 4.7+.

Thanks to
http://lists.pld-linux.org/mailman/pipermail/pld-cvs-commit/Week-of-Mon-20120917/347917.html

So far I have only tested that it compiles.

qca2 was failing to build with:

    building big_ops2.o
    g++ -c -m64 -pipe -O2 -Wall -W -D_REENTRANT -fPIC -DDATADIR=\"/nix/store/yf4ajdx96c8zfprrghqybl5chbnsc4ar-qca-2.0.3/share/qca\" -DQCA_SYSTEMSTORE_PATH=\"/nix/store/yf4ajdx96c8z
    fprrghqybl5chbnsc4ar-qca-2.0.3/share/qca/certs/rootcerts.pem\" -DBOTAN_TYPES_QT -DBOTAN_TOOLS_ONLY -DBOTAN_FIX_GDB -DBOTAN_MINIMAL_BIGINT -DBOTAN_MP_WORD_BITS=32 -DBOTAN_KARAT_
    MUL_THRESHOLD=12 -DBOTAN_KARAT_SQR_THRESHOLD=12 -DBOTAN_EXT_MUTEX_QT -DBOTAN_EXT_ALLOC_MMAP -DQT_NO_DEBUG -DQT_CORE_LIB -DQT_SHARED -I/nix/store/q20l3s8h2scx1kw2hg9y9136wrr8vbf
    0-qt-4.8.4/share/qt-4.8.4/mkspecs/linux-g++-64 -I. -I/nix/store/q20l3s8h2scx1kw2hg9y9136wrr8vbf0-qt-4.8.4/include/QtCore -I/nix/store/q20l3s8h2scx1kw2hg9y9136wrr8vbf0-qt-4.8.4/
    include -I../include/QtCrypto -I. -Ibotantools/botan -I. -o big_ops2.o botantools/botan/big_ops2.cpp
    In file included from botantools/botan/botan/bigint.h:38:0,
                     from botantools/botan/big_ops2.cpp:34:
    botantools/botan/botan/secmem.h: In instantiation of 'QCA::Botan::SecureVector<T>::SecureVector(const T*, QCA::Botan::u32bit) [with T = unsigned int; QCA::Botan::u32bit = unsig
    ned int]':
    botantools/botan/big_ops2.cpp:170:40:   required from here
    botantools/botan/botan/secmem.h:217:50: error: 'set' was not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation [
    -fpermissive]
              { MemoryRegion<T>::init(true); set(in, n); }
                                                      ^
    botantools/botan/botan/secmem.h:217:50: note: declarations in dependent base 'QCA::Botan::MemoryRegion<unsigned int>' are not found by unqualified lookup
    botantools/botan/botan/secmem.h:217:50: note: use 'this->set' instead
    make[1]: *** [big_ops2.o] Error 1
    make[1]: Leaving directory `/tmp/nix-build-qca-2.0.3.drv-0/qca-2.0.3/src'
    make: *** [sub-src-make_default] Error 2
    builder for `/nix/store/snpr8qqn14sz2wsx5plvlflhc73vcm4f-qca-2.0.3.drv' failed with exit code 2