Refactored read_scale(), memio_new(), var_create_dataset() and makespecial()
    to clean up resources properly on failure.

Refactored doubly-linked list code for objects in the libsrc4 directory,
    cleaning up the add/del routines, breaking out the common next/prev
    pointers into a struct and extracting the add/del operations on them,
    changed the list of dims to add new dims in the same order as the other
    types, made all add routines able to optionally return a pointer to the
    newly created object.

Removed some dead code (pg_var(), nc4_pg_var1(), nc4_pg_varm(), misc. small
    routines, etc)

Fixed fill value handling for string types in nc4_get_vara().

Changed many malloc()+strcpy() pairs into calls to strdup().

Cleaned up misc. other minor Coverity issues.