rrdtool: enable perl and python bindings

1. default enable perl and python bindings
2. rrdtool uses perl.real, perl.real doesn't know where the PERL5LIB should be
when prebuilts are used. Use the wrapper perl instead, perl sets PERL5LIB and
invokes perl.real
3. While using dash as /bin/sh, subsequent commands in functions will not use
the environment variables passed to the function call line unless explicitly
run "export ENV_VAR".
4. delete unrecognized options: "--enable-local-libpng" and "--enable-local-zlib"

Signed-off-by: Chong Lu <Chong.Lu@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>