Add an option to hide or show Cache and Buffers in Graph mode

[batk0]

This PR covers issue #407.

[x]    Show cached memory in graph

Added this option to "Display Options". It's enabled by default to be compatible with current behavior. Disabling it will remove Cache and Buffers memory from Memory Graph and Mem&Swp Graph.

[Explorer09]

I expect this PR be rebased on / merged with #928. Otherwise I fear this would conflict with the multi-color graph feature I already proposed in #714.

[batk0]

I expect this PR be rebased on / merged with #928. Otherwise I fear this would conflict with the multi-color graph feature I already proposed in #714.

No problem. I can rebase as soon as #928 is merged. Otherwise I don't know what to do.

[BenBE]

The actual change looks good (should be one commit though, not two), but I'm not very eager about the feature overall.

@fasterit @natoscott What do you think?

[fasterit]

I think for consistency reasons this switch should also affect the bar mode.
I'm not against it, it's small and fits a use case of seeing how much memory is used and not-easily evictable.
/DLange

[fasterit]

As I said on a comment this should also affect bar mode.

The cheap "NaN" stunt causes an assert failure:

stderr output >>>>>>>>>>
htop: Meter.c:409: Meter_humanUnit: Assertion `value >= 0.0' failed.
<<<<<<<<<< stderr output <<<<<<<<<<

The code also needs to save the setting to htoprc and print it in the crash handler (the Settings handling is incomplete).

[natoscott]

@fasterit @natoscott What do you think?
I'm not against it, it's small and fits a use case [...]

I don't love it, as it adds yet another configurable option many people wont need and the Options menu is already cluttered. OTOH I don't see any better solution, so I wont object to it being added.