sar: make buffers that hold timestamps bigger

[msekletar]

On systems that use Korean UTF-8 locale sar will not print timestamp
because there is not enough space in the buffer.

I bumped buffer size to 64 bytes because I figured out that 32 bytes is
still not enough to print out timestamp when using some glibc supported
locales.

$ LC_TIME=ko_KR.UTF-8 ./sar 1 1

Before:

Linux 4.7.2-201.fc24.x86_64 (morgoth.usersys.redhat.com)        2016년 09월 30일   _x86_64_        (4 CPU)

                CPU     %user     %nice   %system   %iowait    %steal     %idle
                all      4.51      0.00      2.51      0.00      0.00     92.98
Average:        all      4.51      0.00      2.51      0.00      0.00     92.98

After:

Linux 4.7.2-201.fc24.x86_64 (morgoth.usersys.redhat.com)   2016년 09월 30일   _x86_64_        (4 CPU)

18시 18분 36초     CPU     %user     %nice   %system   %iowait    %steal     %idle
18시 18분 37초     all      3.76      0.00      2.26      0.00      0.00     93.98
Average:        all      3.76      0.00      2.26      0.00      0.00     93.98