out where to find the technology corresponding to a file given on
the command line: (1) Changed the default search location from
/usr/share/pdk to /usr/local/share/pdk, which is the actual default
for open_pdks (can still be overridden by environment variable
PDK_ROOT). (2) Made the PDK name by itself preferable to the PDK
name plus any extension when searching (e.g., "sky130A" is preferred
over "sky130A_backup"). (3) Check the located directory for any
file <tech_name>.tcl and source it if it exists. (4) Run any tag
callbacks on the "tech load" command, which rebuilds the tool icons.