Use the '-z' option of the 'test' command to check whether 'MSG' is
a string of zero length.

Do not test the variable 'MSG' twice, return '1' by using the
'false' command in the first 'if' statement. In this way the 'push'
target is aborted right after printing the reminder. There is no
need to test it once again.

fix resource leaks

Fix dynamic.c segmentation fault

Make dlopen() use cwd.

Without this fix the program will get a segmentation fault, as
dlopen() will return NULL, and dlerror() diagnoses:

    Failed to load fn.so: fn.so: cannot open shared object file: No such file or
    directory

man dlopen says:

    If filename contains a slash ("/"), then it is interpreted as a (relative or
    absolute) pathname (**what we want**). Otherwise, the dynamic linker
    searches for the object as follows… (*lists several options that don't for
    the cwd unless you set up env vars*)

fix memory leak

fix make target

Because it seems enough compilers allow the latter now.