gmutils – Support macros for other packages

Mis­cel­la­neous macros used by oth­ers of the au­thor’s pack­ages.
Con­tents of the pack­age: \newgif and other glob­als; \@ifnextcat and \@ifX∃TeX; \(Re)storeMacro(s) to over­ride re­def­i­ni­tions; \af­terfi and friends; com­mands from rel­size, etc.; “al­most an en­vi­ron­ment” or re­def­i­ni­tion of \be­gin (\be­gin* doesn't check if the ar­gu­ment en­vi­ron­ment is de­fined).