use the default install prefix on unixes

as documented, this option mainly make sense on windows. On unixes, it is
quite certainly not the expected behavior.

Author: glehmann

.travis.yml

@@ -22,7 +22,7 @@ before_script:
   - cd ${TRAVIS_BUILD_DIR}
   - mkdir -p bin/clBLAS
   - cd bin/clBLAS
-  - cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_TEST=OFF -DBUILD_CLIENT=ON ../../src
+  - cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_TEST=OFF -DBUILD_CLIENT=ON -DCMAKE_INSTALL_PREFIX:PATH=$PWD/package ../../src
 
 script: 
   - make install

src/CMakeLists.txt

@@ -67,7 +67,7 @@ set( CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${PROJECT_SOURCE_DIR} )
 
 # On windows, it's convenient to change the default install prefix such that it does NOT point to 'program files' (permissions problems)
 # Need to check out CMAKE_RUNTIME_OUTPUT_DIRECTORY variable, and see if that eliminates the need to modify install path
-if( CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT )
+if( WIN32 AND CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT )
 	set( CMAKE_INSTALL_PREFIX "${PROJECT_BINARY_DIR}/package" CACHE PATH "Install path prefix, prepended onto install directories" FORCE )
 endif( )