Add "MYSQL_BASE_VERSION" to the list of substituted variables in the "scripts" subdirectory.

scripts/Makefile.am:
  Add "MYSQL_BASE_VERSION" to the list of substituted variables,
  for later (possible) use in "mysql_install_db" and "mysqld_safe".

scripts/Makefile.am

@@ -119,6 +119,7 @@ SUFFIXES = .sh
 	  -e 's!@''innodb_system_libs''@!@innodb_system_libs@!' \
 	  -e 's!@''openssl_libs''@!@openssl_libs@!' \
 	  -e 's!@''VERSION''@!@VERSION@!' \
+	  -e 's!@''MYSQL_BASE_VERSION''@!@MYSQL_BASE_VERSION@!' \
 	  -e 's!@''MYSQL_SERVER_SUFFIX''@!@MYSQL_SERVER_SUFFIX@!' \
 	  -e 's!@''COMPILATION_COMMENT''@!@COMPILATION_COMMENT@!' \
 	  -e 's!@''MACHINE_TYPE''@!@MACHINE_TYPE@!' \