turn sharing back on

It doesn't make much difference in timing now:

"coqdep" -c -R . Ktheory "Utilities.v" > "Utilities.v.d" || ( RV=$?; rm -f "Utilities.v.d"; exit ${RV} )
"coqdep" -c -R . Ktheory "Categories.v" > "Categories.v.d" || ( RV=$?; rm -f "Categories.v.d"; exit ${RV} )
: compiling Utilities.v ; >Utilities.timing \time -f "%U sec, %M bytes: Utilities" coqc  -q  -R . Ktheory -no-native-compiler -indices-matter -time  Utilities
0.11 sec, 431751168 bytes: Utilities
: compiling Categories.v ; >Categories.timing \time -f "%U sec, %M bytes: Categories" coqc  -q  -R . Ktheory -no-native-compiler -indices-matter -time  Categories
2.07 sec, 1385938944 bytes: Categories
./Categories.v:27639-27703: [exact~(assoc~_~_~_~_~_~(Coprod...] 0.477 secs (0.476u,0.001s)
./Categories.v:27704-27708: [Qed.] 0.231 secs (0.23u,0.s)
./Categories.v:38189-38197: [Defined.] 0.166 secs (0.166u,0.s)
./Categories.v:38047-38184: [exact~~(Abgr.Product.UniqueMap...] 0.114 secs (0.113u,0.s)
./Categories.v:20244-20248: [Qed.] 0.114 secs (0.114u,0.s)
./Categories.v:38018-38040: [apply~El.mor_equality.] 0.05 secs (0.05u,0.s)
./Categories.v:37839-37865: [destruct~T~as~(T_ob,~T_el).] 0.044 secs (0.042u,0.001s)
./Categories.v:20156-20175: [apply~mor_equality.] 0.035 secs (0.034u,0.s)
./Categories.v:17094-17117: [End~StandardCategories.] 0.032 secs (0.029u,0.003s)
./Categories.v:20204-20223: [apply~mor_equality.] 0.03 secs (0.03u,0.s)

real	0m2.532s
user	0m2.257s
sys	0m0.275s