ash,hush: optional support for $HISTFILESIZE.

ash,hush: optional support for $HISTFILESIZE.

Based on patch from Alexey Fomenko (ext-alexey.fomenko AT nokia.com)

function                                             old     new   delta
size_from_HISTFILESIZE                                 -      44     +44
hush_main                                            998    1025     +27
ash_main                                            1348    1374     +26
read_line_input                                     3361    3372     +11
new_line_input_t                                      17      24      +7

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>