In the cases where the actual result is "v2, v2" instead of one
implementation being used directly and another indirectly (think:
demo-app/wheezy with libkdecore5/squeeze), providing a base symbol in
libcallee.so.2 makes libcaller behave as expected again. It helps.
On the other hand, in the cases where the actual result is "v1, v1"
instead of the expected mixture of implementations (think:
demo-app/squeeze with libkdecore5/wheezy), there's nothing we can do.
Luckily, in the case of liblzma, _all_ routines from liblzma2 work
just fine as implementations of the liblzma5 ABI, since the only
possibly relevant ABI mismatch is the added padding at the end of the
lzma_stream struct, which liblzma2 happily ignores. So libcaller
behaves just fine, and we are safe, barely.