More small changes for 4.2

I would like to let you known about 4 small improvements made following to discussions that occurred few months ago on the mailing-list or on bug trackers.

New --with-bin-search-path configure option

New ./configure option added to get in control of the path list used to search the tools required to build and configure Modules (like ps and basename). Default value is /usr/bin:/bin:/usr/local/bin.

New --enable-silent-shell-debug-support configure option

New ./configure option that adds the ability to control whether or not code to support silent shell debug should be added to the module function and sh-kind initialization scripts. Enabled by default.

Useful for those wanting a small and neat module shell function definition (by use of the --disable-silent-shell-debug-support option).

New --enable-quarantine-support configure option

Following same target than the previous new option, this one adds the ability to control whether or not code to support quarantine mechanism should be added to the module function and initialization scripts. Enabled by default.

Express Modules compatibility of modulefile with versioned magic cookie

Any modulefile should start with the #%Module magic cookie and sometimes a version number may be placed right after this string. Until now this version number corresponded to a modulefile format version but it was never checked.

Now this version number reflects the minimum version of Modules required to interpret the modulefile. If the version number is set along the magic cookie string it is now checked and the modulefile is interpreted only if Modules version is greater or equal to this version number. For instance, if a modulefile begins with the #%Module4.3 string, it can only be evaluated by Modules version 4.3 and above. Elsewhere the modulefile is ignored like files without the #%Module magic cookie set.