fixed INSTALL_DIR variable name typo
changes to achieve compatibility with Vivado 2014.1:
single ended IOSTANDARD for XADC inputs (fixes error during bitstream generation)
synthesis advice for dfilt1/r3_reg to use DSP for the summation (fixes large timing violations caused by long carry chains - Vivado 2013.3 / ISE 14.6 synthesised the DSP without the hint)