Check for ODBC headers in addition to checking for odbc_config tool

cmake/FindODBC.cmake

@@ -5,6 +5,19 @@ find_program(UNIX_ODBC_CONFIG odbc_config
 	/usr/local/bin 
 	PATHS)
 
+# Check that we can find the ODBC headers in `odbc_config --include-prefix`
+# location If the headers cannot be found, set UNIX_ODBC_CONFIG to
+# UNIX_ODBC_CONFIG-NOTFOUND since the odbc_config tool is essentially useless
+# if `odbc_config --include-prefix` doesn't actually point to ODBC headers
+if(NOT ${UNIX_ODBC_CONFIG} MATCHES "UNIX_ODBC_CONFIG-NOTFOUND")
+	execute_process(COMMAND ${UNIX_ODBC_CONFIG} --include-prefix
+                        OUTPUT_VARIABLE UNIX_ODBC_INCLUDE_PREFIX
+                        OUTPUT_STRIP_TRAILING_WHITESPACE)
+	if(NOT EXISTS ${UNIX_ODBC_INCLUDE_PREFIX}/sqlext.h)
+        	set(UNIX_ODBC_CONFIG "UNIX_ODBC_CONFIG-NOTFOUND")
+	endif(NOT EXISTS ${UNIX_ODBC_INCLUDE_PREFIX}/sqlext.h)
+endif(NOT ${UNIX_ODBC_CONFIG} MATCHES "UNIX_ODBC_CONFIG-NOTFOUND")
+
 if(${UNIX_ODBC_CONFIG} MATCHES "UNIX_ODBC_CONFIG-NOTFOUND")
 	message(STATUS "Couldn't find unixODBC")
 else(${UNIX_ODBC_CONFIG} MATCHES "UNIX_ODBC_CONFIG-NOTFOUND")