Protected the definition of the plGetDrvDir function with #ifdef ENABLE_DYNDRIVERS. This avoids potential compilation problems with DRV_DIR not being defined when --disable-dyndrivers is given to configure.
Protected the definition of the plGetDrvDir function with #ifdef
ENABLE_DYNDRIVERS. This avoids potential compilation problems with DRV_DIR
not being defined when --disable-dyndrivers is given to configure.

svn path=/trunk/; revision=4757

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot