add missing dropin.cache file required by default spidermanager tests

scrapy/tests/test_contrib_spidermanager/dropin.cache

@@ -0,0 +1,71 @@
+(dp1
+S'spider2'
+p2
+ccopy_reg
+_reconstructor
+p3
+(ctwisted.plugin
+CachedDropin
+p4
+c__builtin__
+object
+p5
+NtRp6
+(dp7
+S'moduleName'
+p8
+S'scrapy.tests.test_contrib_spidermanager.spider2'
+p9
+sS'description'
+p10
+NsS'plugins'
+p11
+(lp12
+g3
+(ctwisted.plugin
+CachedPlugin
+p13
+g5
+NtRp14
+(dp15
+S'provided'
+p16
+(lp17
+cscrapy.spider.models
+ISpider
+p18
+asS'dropin'
+p19
+g6
+sS'name'
+p20
+S'SPIDER'
+p21
+sg10
+NsbasbsS'spider1'
+p22
+g3
+(g4
+g5
+NtRp23
+(dp24
+g8
+S'scrapy.tests.test_contrib_spidermanager.spider1'
+p25
+sg10
+Nsg11
+(lp26
+g3
+(g13
+g5
+NtRp27
+(dp28
+g16
+(lp29
+g18
+asg19
+g23
+sg20
+g21
+sg10
+Nsbasbs.