AMIGAOS: Cleanup

Comments cleanup and one case of a misused TAB
CONFIGURE: Ask for unity >= 3.8.1
Previously we asked for unity == 3.8.1, which broke things everywhere else
CONFIGURE: Use pkgconfig to get CFLAGS for Unity if not supplied

This is not necessary if we got --with-libunity-prefix= (line
1447).
That's not always the case though.
AMIGAOS: More cleanup

Another case of misused TAB
AMIGAOS: More cleanup

Period on all comments
Merge pull request #511 from tobiatesan/unity

CONFIGURE: Fix support for libunity in configure
Merge pull request #510 from raziel-/patch-3

AMIGAOS: Cleanup
CGE2: Fix a crash when detecting an empty set of VOL files
CGE: Fix a crash when detecting an empty set of VOL files
VIDEO: Fix seeking in AVI videos with no initial audio frames
CGE2: Silence gcc warnings
SAGA: Silence a gcc warning
FULLPIPE: Silence a gcc warning
CGE2: Remove unused constants
CGE2: Fix the case of a couple of constants, remove a useless variable
CGE2: Constify strings
CGE2: Initialize some variables
MADS: Rex - Fix safety check in ASound9
MADS: Rex - Remove unused variables
CGE2: Initialize a variable