Require configure prefix to be set
Added consistency for setting install path

- for configure, the install directory is <prefix>/genesis-2.4
- for Makefile.dist, introduced PREFIX variable:
  `PREFIX=<path> make install` installs to <prefix>/genesis-2.4
- in both cases, can override target path by calling
  `INSTALLDIR=<path> make install`

Also, fixed travis-ci rule (don't use relative path for configure!)
Optimisation for configure builds

- CFLAG += -O2 now standard optimisation
- removed libSM, libICE where not needed on modern platforms
Merge pull request #24 from physicalist/master

Require configure prefix to be set