Previously, if we attempted to build using C99 or later, we got "inline
function declared but never defined" warnings and eventual "undefined
reference" errors. As a result, it fails to build from source using gcc5.
However, if we move the definitions to list.h and add "extern inline"
declarations to list.c, which does compile using C99 and later, then it no
longer compiles using gnu90, the default for gcc4.
To avoid this mess, we remove the inline keywords altogether.
Note that this fixes Debian bugs for wmifs [1], wmppp.app [2], and
wmtime [3].
[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=778170
[2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=778172
[3] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=778174
