Fix Bug 9725 'Lua: ProtoField.new() is buggy'

Using ProtoField.new() is dicey.  Many of the optional arguments don't properly check the lua stack - they call lua_isnil() for their index number, instead of lua_gettop() to see the stack size.  lua_isnil() may return false in such cases.

Change-Id: I83ca1e5fc34e71ec35899adbedabcee69571b9fe
Reviewed-on: https://code.wireshark.org/review/118
Reviewed-by: Stig Bjørlykke <stig@bjorlykke.org>
Tested-by: Stig Bjørlykke <stig@bjorlykke.org>
Reviewed-on: https://code.wireshark.org/review/207
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Fix Bug 9728 'Lua: ProtoField.bool() VALUESTRING argument is not optional but was supposed to be'

Similar to bug 9725 and ProtoField.new(), the way the VALUESTRING argument is being checked
in the code for ProtoField.bool() ends up making it non-optional.  This patch fixes that,
along with some minor API documentation fixes (text).

This is a backport for change-id Iadb9a8ace9c5514fc623d882301fe16b637fe4ce

Change-Id: Ic60375f3e0ad7c7a8887dce7ffbd946f0a9d80b5
Reviewed-on: https://code.wireshark.org/review/209
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
[Automatic manuf, services and enterprise-numbers update for 2014-02-16]

Change-Id: Id8a7fe6a64184a121c945c8cd281863b96dd233e
Reviewed-on: https://code.wireshark.org/review/230
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Alexis La Goutte <alexis.lagoutte@gmail.com>