I have checked in support for C99 inline function declarations--these are now the default in gcc 4.3 when compiling with -std=c99. Previously the GNU 'extern inline' extension worked in C99 with gcc but now it is more strict [1].
The new header file <gsl/gsl_inline.h> defines some macros which change the inline declarations. It needs to be included in any header that uses inline functions. The static versions of inline functions in libgsl.a are now made by compiling the header files (with the macros in "build.h"), so the code only appears in one place rather than being duplicated in the .c files. [1] http://gcc.gnu.org/gcc-4.3/porting_to.html
