Add some info about feature test macros.
Heed the new advice.
Merge branch 'master' into more-gcc
Let `ioFileType()` optionally follow symlinks.
I reversed the sense of `stat` vs. `lstat`. Fixed!
Add a directory, to help validate directory enumeration.
Don't rely on `dirent.d_type`.

It's not sufficiently standardized, alas.
Add feature test, so that glibc will be happy.
`dirent.d_namlen` is also not standardized.
Add required `#include`s.
`sigjmp_buf` requires a feature test macro definition.
More feature test fun.

Added comment to `Jump.h` to explain what's going on here.
One more feature test.
Merge pull request #762 from danfuzz/more-gcc

More gcc / glibc work