fix compilation on mips

For mips64 and mips64el, they use -mabi=64 instead of -m64.
Thanks to Yunqiang Su for the patch (Debian #747431).
Merge pull request #303 from satta/mipsfix

fix compilation on mips
clean up public API and exported symbols in shared library
src_clean
add libtre to list of shared libs
fix GtRecMap API
avoid error message on Mac OS X
cosmetics
Merge pull request #304 from satta/exports

clean up public API and exported symbols in shared library
src_clean, copyrights
"allows to" -> "allows one to"
fix compilation with shared libs

Some libraries required when building GenomeTools using shared
dependencies were not added in the linker call, leading to
problems later on. Examples: libm, libpthread.
disable use of xmllint for manpage generation

This fixes some weird issue when building Debian packages.
make public symbols list creation more portable
src_clean
update documentation
Merge pull request #305 from satta/smallfixes

Small fixes