Merge pull request #193 from agtorre/master

Merging small file into master to tag 2.3.1rc1
Merge pull request #194 from agtorre/master

added an extra header to LogMessage.h to make it compatible with gcc 4.7.2
Add virtual destructor for IOSHandle and IOSDirHandle.

The destructor should be virtual so that when a base pointer is
deleted, the correct destructor can be called.
Add prefix to metalinks in order to compare them correctly.

According to line 832: prefix should be included in metalinks.
So when we get the content of the links, we should use exactly
the same way to construct the string 'tmp' as 'shadow'. Otherwise
the comparison is incorrect.
Add PLFS source code directory to the front of LDFLAGS.

Otherwise old plfs library in the system might break the build
process.
Merge pull request #195 from zhang-jingwang/master

Two small fixes for IOStore and metalink.