Replace dd usage to head+tail

[slonm]

Based on my fall into incompatibility dd call in makeself v.2.2.0 with busybox on Synology and extended investigation dd usage on stackexchange.

As result i rewritten only MS_dd() while MS_dd_Progress() is not needed for my purposes:

MS_dd()
{
    <\$1 tail -c +\$(expr \$2 + 1) | head -c \$3
}

Incompatibility caused by dd support ibs/obs parameters Then i found the issue is known #161 and fixed https://github.com/megastep/makeself/commit/9504cc4c7f30d10fef9603396c5cd4913c192eed as bulky patch with check dd parameters support and the patch fixed only MS_dd() too. MS_dd_Progress() left untouched too. I could rewrite both functions without dd usage. Let me know if it makes sense to anybody and i'll do it.