augeas: fix augprint -h segfault

[ZhongRuoyu]

This was caused by a missing #include <libgen.h>. It was resolved in hercules-team/augeas#792, together with the 'malloc.h' file not found error.

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[ZhongRuoyu]

Actually, on second thoughts, I think I can improve the test a bit. This should help us to at least detect some trivial errors.

[BrewTestBot]

@p-linnane has triggered a merge.