if fmm not installed, have kernel routines set fmm to empty.

[askhamwhat]

• like the title says, don't load fmm info into kernel if it doesn't exist on path
• put try and catch in fmm wrappers for various kernels
• print warning if forcefmm used in any routine and fmm not available

[mrachh]

This issue is closed with commit c0f4af8