Fix ambiguous and confusing use of "entry" in palette device member names
related to indirection. Array m_indirect_entry is now m_indirect_pens.
Getter indirect_entries() now returns the number of indirect colors, which
is more useful than the number of indirect pens (the latter is always
either zero or equal to the palette size, depending on whether indirection
is being used at all)

Fixed debug assert: rgb_t isn't POD according to GCC 4.8, so we can't use
resize_and_clear. Use append() instead to dynamically expand m_indirect_colors.
This change also ensures that indirect_entries() returns the actual number
of indirect colors, not rounded up to the next multiple of 256.

Thanks to these changes, the OSD palette viewer now displays the indirect
colors correctly once again.

Added MCFG_PALETTE_INDIRECT_ENTRIES to all games using indirection in seta.c.
This change should fix all color regressions in that driver.